Okay, checked again on 350 and you are right, there is no FF button. But I then remembered my previously successful method: a slight swipe of the "scrubber" (not really holding, more sweeping) to the right yielded near perfect results 6/7 times and skipping almost exactly past the commercials. Not sure if it was pure coincidence/luck though

I'm sure there's a secret way like the triple/quadruple tap from the old IFE's, but haven't found it yet.