Unfortunately it doesn't appear so. I have done extensive flower animation in PFX and have long wished for this feature. The features--leaves, petals, etc--don't appear to be independent nodes. What you may be able to do is convert the brush to polys, select the 'flower' object and do poly>separate which will break up the individual shapes. If you leave construction history on, and depending on the amt. of tweaking you do to the resulting shapes, the PFX animation may be preserved. Good luck, let me know if anyone has found a better method.
Sean