Create a movie clip (MC) starting out with the look of it when it's mouseover'd. Do what you like with the rest of the frames in that MC as your animation. Then throw the MC in the HIT frame of your button. Basically you're emulating it again, but there's a whole MC behind the HIT and not just a simple effect like your mouseover.
Don't forget to put a stop() action in the MC though.

Flash is very time-consuming isn't it? Even with Swish, you'll have to putz around with placement after importing it (if you're importing into Flash at all).