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.