If it's a game the PC:s are engaged in, both options you mention can work really well. As long as the chained events are given as a premise at the beginning, the players should not feel that it's cheap. However, the question was more about how to camouflage the chain.
The faux choice
This is like a magic trick in that it can feel cheap when you know the trick, but still looks good from the outside.
Let's say that the wizard gives the players three scrolls. Each scroll contains an assignment, but the only thing they can read without breaking the seal is the location of the assignment. They now have three different assignment locations and get to choose in which order to complete them.
However, the assignments you have prepared always come in a certain order. The players only choose where they take place. This makes it possible for you to chain the events any way you want, but you add an element of false choice.
Afraid that the PC:s will open all scrolls and then choose what order to do them in? The wizard can hold on to the scrolls and only give them their chosen one. If you want them to have all scrolls, make them choose the order before leaving the wizard. The wizard now enchants them so that the second scroll cannot be opened before the first scroll is completed.
You can have the wizard do this by himself, but it feels more natural if you have more people that he can discuss with. Let's say nine wizards instead.
The PC:s are only given one task. The specifics of the task should be a bit open for interpretation and upon completion the committee of wizards cannot agree on if the task was completed or failed. In order to resolve it, they give the PC:s a new task. As this goes on, it can become apparent that the wizards are only playing with the PC:s. Deal with the shenanigans of the wizard or forfeit the substantial reward.
Chain the chains
The wizard gives out a number of assignments at once. When they're completed, the PC:s will have to go back for more. The trick? The assignments given can be completed in any order, but it is fairly obvious that there is a preferred order.
- A corrupt nobleman has a prized statue. There are a lot of guards and wards though and fighting will most likely break out.
- A low level thief just came over a powerful set of enchanted lockpicks. Steal them from the apartment.
- In a vault in the bank there is an amulet that grants massive buffs. The bank has few guards since they recently installed high security magical locks.
The lockpicks will be useful in the bank and the amulet will tip the balance in favor of the PC:s when fighting. When the PC:s return with all three items they recieve a new package of assignments.
Reverse the chain
Give the PC:s the last assignment. While attempting it, they find they need something else first. In order to procure this item they first need to... You get the drift. The PC:s have one step to complete, but in order to complete it they need to complete another step.
This can feel a bit forced, but I've always preferred it as a player since I always have a clear goal in sight. It also lends itself well to altering or bypassing events if needed.
As a GM, I do a lot of railroading. Sometimes I do it without planning for it. About two years ago I wrote a one-shot adventure where I thought the players had plenty of options, but each group I played it with went the exact same route. It might have been a coincident, but I think a more likely explanation is that the events had a logical order of increasing resistance. Searching through the room in the mansion you're already in is simple. You would rather go to the apartment of the missing person to look for clues first, rather than the place where she works. And so on.
Chains are hard to cover up, especially since they're very common and the players will recognize them easily. The key here shold not be to try to hide the chains too much, but make them more comfortable to bear.