Since the LM2577 is supposed to have self-limiting current control, I can't think of a reason not to be able to parallel the outputs. Course, you'll have to make sure your input can easily supply the power you're looking for.
Now, to be on the safe (or conservative) side, you might want to put a hefty cap (electro, tantalum, maybe even a supercap [dpending on the output voltage]) on the output to "smooth out" current transitions.
That might also subdue, as Dr pepper resaonably suggests, any mad oscillations that rear their ugly heads...
Can't seem to find a PSpice SIM LM2577 to test the idea.