I was working on an NPC summoner for our 4E game this week and am a bit mystified. Given that controlling a summoned creature requires a standard action and characters only get one standard action, only one summoned creature can be directed per turn (though there are a few with "default" actions). Ignoring the theme & logistics of this design decision, is there any feat/power/combination that would enable a summoner to direct more than one summoned creature per turn?
From an NPC side, the best decision is to call the person a summoner, but have them summon fully-fledged enemies as a standard. The enemies will come out of the encounter budget, and generally would work like a standard encounter.
From a PC side, there are many feats to assist in the action economy. The Druid's creatures all come with an instinctive action, allowing a very hands-off approach. The Druid Commanding Form feat provides a free minor-action for summons. And the Druid's Epic Primal Summoning Expertise allows a free standard as minor action.
The Wizard Tome of Forty Steps provides a free move.
The thing to remember is that a summoned creature will be doing more damage than an equivalent at-will. If it does less, then the action cost will be reduced to, for example, a minor action. (See the remarkable Artificer power Animate Arbalester). Also note that various class features can inform the capability of summons.
Commanding the Creature in Arcane Power (page 99):
As a minor action, you can command the summoned creature to take one of the following actions, if it is physically capable of taking that action: crawl, escape, fly, open or close a door or a container, pick up or drop and item, run, stand up, shift, squeeze, or walk.
So if by "direct" you mean "tell them what to do" you certainly can direct more than one a round. If you mean "direct them to attack", though that is different.
Usually the attack actions require a standard action from the summoner because the summoned creature is the vehicle for the summoner's attack and that is by design. Getting more attacks in that way would require high level time altering effects. If you want multiple attacks in a round, you can move the the summoned creature to maximize the chances of opportunity attacks occuring.
If the summoner is an NPC, you're basically free to do whatever you like because monsters (including NPCs) don't have to follow the same rules as PCs.
There are already several examples for this. One example can be found in the Scales of War adventure Den of the Destroyer[DDI] where an Elf bounty hunter NPC uses 2 figurines of wonderous power to summon 4 (!) creatures that act as individual monsters and are not dependent on their master's actions.
If - for whatever reason - you need a rules conform way of doing that you could easily give the summoner a special ritual that allows his summons to act on their own. Of course, this ritual would require components that are unavailable to the players (virgin sacrifices, etc.). ;-)
Since you seem to talking about an NPC, you might want to try a magic item of some type. Maybe something like a wand or staff that changes the control action requirement to a minor action on the summoned creature.
This would give the NPC a stronger impact in each round. Give the item a restriction of some type so the party can not use it.
They can still convert it to residuum or, the item can be some part of the story line and the party has to deal with it, if they can. This would give the item a reason for existing.