The way he describes it it goes as Side Control -> Transition to modified rubber guard -> gogoplata I do believe. So it's technically not a gogoplata from side control, it's a transition to it from side control though... thought I'm still not entirely clear on the "Leg up like you're going to half guard then over the shoulder....etc" part. To me it sounds like if they're on your right side you would use your left leg to go over their shoulder and secure rubber guard, but then you have no entrapping leg on their right side... so they could easily just spin out. If they're inexperienced grapplers though it may be possible as a gogo is a very "HOLY SHIT I'M DYING" submission. It's one of those where, if you're not used to it, you want out ASAP.
Also, if you get your leg over their back like that, why not just post for a sweep/stand up or take their back?
meh i was gassed so i just went for it, moral of the story is bjj guys are way worse than having a big wrestler on you, unlike the fitchs and sonnens would have you believe.