There are 2 MOSFETs which do pre-cocking: the BTC Chimera and Burst Wizard claim it for the new BW3 of theirs. I have one, but my PP-19 Bizon 2 has an electrical fault of some kind, otherwise I was going to fit it this weekend. I'll need to get to the bottom of this fault first, because you have to tune them, by trigger pulls in the right timing/order, so that instead of active breaking causing the cycle to complete and stop, an adjustment advanced in a few millisecond increments allows it to run on long enough to cock for the next shot. There is also a tolerance to judge to take account of falling voltage - if BWKK MOSFETs are anything to go by, I'm not expecting it to be at all easy to get right, but you can see why I'm not even going to bother until there's no possibility of an electrical fault...
But yeah, I've seen that L85 gb in action - Mark Walker has one, for those who know him. It's impressive.