>>>Is this in addition to your other options in a round?
If you mean can you use a stunt to effectively conjure up the equivalent of another encounter power, I believe the answer is "yes." Subject to plausibility and suitability of the battle-space and terrain and features and the like.
PS, while it works for many stunts pretty easily, it doesn't really tell you how to resolve others, like "I grab the tall flag-standard, hold it crosswise across my body, and charge the four minions with it, using the standard to push them all back over the edge of the pit."
I don't know if it has a framework for that sort of thing. Following the basic rule of "try to say yes" I guess you'd just call it a multiple-target bull rush with a penalty of (say) -2 per additional target, Str vs. highest Fortitude. If you pull it off, I guess they all go flying into the pit of lava. Or maybe you just roll against each of them individually, taking a -4 penalty (as you're pushing four figures). I dunno.
The framework, as written, and as far as I read (skimmed), really only handles the simplest sort of "inflict damage upon one target" sort of stunt.
That is 90% of them, tho.
Given the basic spirit of "Say Yes to Stunts," tho, I think you're supposed to allow most plausible action hero stunts like this.