Upload & Sell: Off
Umm, the only Profoto modifier that a third-party light can't use is the basic reflector line...zooms and magnums, essentially. Since most everything else uses speedrings, you can conceivably mount them to any brand of light. Hell, beyond a handful of zoom and grid reflectors I don't own a single Profoto modifier, not even an umbrella - it's all Photoflex, Mola, Chimera, Westcott. Most of us aren't brand zealots, we just use what works for us.
As far as mounting Paul's modifiers to Profoto heads - other than for a chuckle, why would you want to do that? I mean, as I understand it, his foldable softboxes are the only proprietary mods...the rest are just inexpensive softboxes and umbrellas. I can already put a cheap softbox, with or without a Buff logo on it, on a less-cheap head and still fail to see the novelty value in that. I might even be able to power my Acute2 packs off a Vagabond - don't see why that's funny either, it's just another way to get a shot.