[Anaraxes]

You could also have the wizard Wait. His Wait condition could be always true. ("No matter what the target does..."). He then casts his spell; then knight goes; then mooks go.

Remember, there's no global turn that affects everyone. You don't begin a turn, have everyone act in sequence, then end the turn, and begin a new one. Turns are individual. The point of the sequence is simply to make sure that there is some order in which everyone gets to conduct one maneuver. You want to avoid double actions where someone goes "last in the turn" and then "first in the next turn".

That being the case, you could also just houserule than you can choose any sequence number you like up to your Basic Speed. You just can't change it in a given combat once you make that choice.

It's not terribly unreasonable for coordinated action between two independent actors costing you some freedom and efficiency. You have a plan; the wizard doesn't carry out your part, then in a one-second interval, you're probably still mentally swearing at him and figuring out what to do instead. Your player can take five minutes to gaze at the tactical map and come up with an alternate plan from scratch, but your character can't. On your next turn, you're likely not to Wait for the wizard again since he's proven untrustworthy, and can indeed do whatever you want. If you want to Wait again for the wizard to do what you want him to do, then again you're giving up your freedom of action while everyone else keeps acting, waiting.