From what I have heard and always understood to be aviation law, you cannot operate ETOPS with only a frozen ATPL. i.e you might be on the BA 757/767 fleet but you are not allowed to fly the 767s on ETOPS route (i.e over big oceans - so no NYC flights). This therefore rules you out of flying 777s until you unfreeze your licence. However, I thought 747s were not ETOPS by the mere definition of Extended range Twin engine OPerationS. 747s have 4 engines (pointing out the obvious), hence in theory you can fly them with a fATPL - not quite sure why you would want to though, wouldn't it be better to hours build and gains lots of experience doing shorthaul first.
Anyway, as I said, this is just what I understood to be the situation - I may well be, and probably am, wrong.