Fuel, fuel, fuel.......
I agree the 'Tailgating' theory is do-able. Is it likely..? No. Too much organisation required to be in the right place at the right time. Way back at the beginning, as soon as the westerly Radar position was revealed, it was clear that the extended westerly flightpath headed for Somalia/Yemen and that a HJ was most likely. Both lawless areas with no ATC/Radar and an all oceanic flight to get there. A little dogleg to the south maybe, to avoid Ceylon. What killed the theory then, was the reported range. However, owing to fuel prices, the a/c may well have had a LOT of fuel on board than we all thought at first. Remember there were also 50 empty seats.... Of course, there were no Somalis on board, but it's an ideal place to take a big a/c without it immediately appearing all over the web. They could unload what they wanted and dump the a/c in the sea, - or just refuel it if they had another nefarious purpose in mind. I think dumping it is more likely.
Personally, I don't suspect the pilots. Whoever did this almost certainly managed to get through the door. The timing of the start of the incident is circumstantially suspicious. If the perps were after all or some of the passengers....there may be surprise happy-ending even yet. If they were after something in the hold....
I'd still like to know what the actual fuel available was.