Lots of engines have this. As example in the Novarossi crankcase as with many brands there is a flat round spot at the side of the carb you can drill out for mounting a nipple. SH (and Force) does have some models with this nipple and a chamber in the rear backplate. connected with a a piece of tube.

But maybe I have missed it, where is it written that this Picco has a boostchamber?