Well, something like this, as a naive implementation:
Mob of Instant Martians: Fair (+2) Minion - Stress: (1) (2) (3)
Strong (+4) at: Brute Force, Massed Fire; Weak (=0) at: Close Analysis, Original Thought
Let's take that as a starting point to talk about some things.
First, an assumption you're probably going to have to make: a single rank-and-file Instant Martian is not going to have any narrative importance; contrariwise, an Instant Martian with any narrative importance is not going to be rank-and-file. You've hit the reason why, of course: if any Instant Martian is a character in its own right, skill pyramid and right to an action in conflict and all, then odds are going to heavily favor the side that can print the most Instant Martians, and that's not usually going to be the side the movie is about.
And that's how these things are, isn't it? If you're going to print a whole bunch of things, why print a whole bunch of smart but expensive things most of which, statistically, you won't even use? Print a whole bunch of cheap and dumb things marshaled by a very smart, very expensive thing. When the stress track of that mob of Instant Martians up there gets filled, that doesn't mean every last Instant Martian went up in a charred puff of green fuzz; that just means that whatever Instant Martians are left are too few and/or too disorganized to present a meaningful threat.
This is not to say that everyone who uses Instant Martians only uses Instant Martians and never any actual purpose-built Martians as security or observation or research personnel, who do have their own skill pyramid and right to actions in a conflict. But it's like... well, imagine you're architecting a corporate building. Do you make every element of the building, walls and windows and doors, interior and exterior, out of military-grade reinforced materials? Do you throw luxe and shine and plush and polish onto any surface that'll hold some? Who has ever? You luxe and harden the C-level suites, you luxe up the public-facing places, you harden research or central processing or whatever makes you the real money, and for the rest you just worry that it takes the weight and is cheap to maintain. How luxe and hardened the 6th-floor HR supply closet is will never matter.
Until the PCs smuggle themselves in disguised as a shipment of toner, I mean. But that's the point: Fate is dramatic. Fate isn't about the way things are usually done. Nobody who built Nakatomi Plaza was thinking "but what if, someday, a Die Hard?"
Instant Martians take the weight and are cheap to maintain, but around the things that really matter there will be agents with pyramids and actions, who are not rank-and-file Instant Martians.
But what if I want Instant Martians?
Well, it can be useful to model it as a combination of the summons from the High Fantasy Magic rules and the much older concept of attached minions from Spirit of the Century-era Fate "3.0". Essentially, you decide on your Instant Martians' turn whether they're providing you a teamwork bonus or acting on their own, and if they provide you a teamwork bonus, they also take the first bit of damage you would take and are dispersed.
So a stunt like:
Moption. When you have time to replenish and rehydrate them, you can begin any conflict with an allied fire team of Instant Martians. They have +1 to Shoot and one box of Stress.
isn't too far off in power from basic stunts, being about +1 to attack and create an advantage with Shoot until you take damage, if you use them exclusively in attached mode.
But how do you deal with attempts by players to get larger and more imposing backup squads of Instant Martians? Well, within limits, Atomic Robo's invention setup isn't a bad idea. You want to be able to, effectively, stack a certain number of free invokes on the Instant Martians you create, which you then burn to improve the stress they can absorb and the skills they have access to. But doing that feeds Fate Points into the GM reserve equal to that boosted number, and the Instant Martians are still susceptible to damage and may be more difficult to replenish depending on how you look at invention complications.
But what if the bad guys actually have 10,000 Instant Martians?
That's not really something a handful of PCs can deal with at a conflict level. Either they turn into units on a larger scale of conflict, or you treat them as obstacles the PCs have to overcome rather than seize the fate of and destroy. Pilot your ship down to the surface of the ACME corporate homeworld, under the withering blaster fire of 10,000 Instant Martians! Infiltrate through the attractively thick and toxic ornamental jungle, patrolled by 10,000 Instant Martians! Drive your cyber-form through to the heart of the ACME mainframe, defended by 10,000 Instant Martians on keyboards! (The overall structure is kind of a hybrid of contest and conflict, where there isn't really anybody but you to get overstressed; you're being attacked by an obstacle that you can't attack back while you try and rack up the successes that represent contest progress.)