Dragon Age's design philosophy is that "random events" (stunts) happen so often that you might actually plan them; you just can't specify exactly which combat round they'll be executed.
The most straight-forward way to add player control over this is indeed by banked stunt points.
There's nothing wrong by adding rules that allow you to perform moves similar to stunts by the way of making ability tests. Indeed, that is how many other games have done it through decades of roleplaying.
However, you do lose (some) of the inventiveness and uniqueness of the AGE system if you do add "back" this into the system, and I personally recommend that you do not do it just as a reflex, just because you're accustomed to how things work elsewhere. Indeed, I would recommend that you hold off adding back rules for ability tests to perform special combat maneuvers until you have tasted the unique way of how AGE does things...

One compromise approach would be to allow a special action to generate stunt points in general, and then use the stunt charts normally.
That is, instead of taking a specific action (with a lot of rules for how different actions trigger different Ability Tests, just like in other fantasy rpgs) instead of dealing damage, you take the general "generate stunt points" action, which, if the Test is successful, generates as many Stunt Points as the Dragon Die indicates, possibly with a small bonus. Then you use these Stunt Points to see if you can afford to pull off the desired special action, or if you will have to settle for some lesser Stunt.
The advantage is that you avoid having two systems that share the same "design space", that are made (more or less) for the same purpose. The Stunt mechanic is clearly designed to
replace the list of special actions of other games; why not acknowledge and embrace that when playing AGE?
At least, if you do choose to go ahead with a special maneuvers subsystem, make it an informed and deliberate decision rather than a knee-jerk reaction to missing what you've grown accustomed to*!
Cheers and good luck with your game!
*) Not saying this applies to you reading this - only that I identify a possibility that a gamer might adding back what they perceive as "missing" without seeing the value in its deliberate omission 