Dark Eldar transports are open-topped, so the whole damn thing is an access point. No feeding frenzy possible, there.
I, also, have precious few success stories to tell. Generally, the tactic is just too much trouble to pull off to be worth it. Most of my opponents don't run terribly mechanized lists (with the exception of the Eldar and, occasionally, a Sisters list), so an 'expensive unit in a transport' is a rarity. Even when it does show up, it is typically more practical to blow the thing up than wait the extra turn to set up/execute the Frenzy. Entangled Terminators in the open are just as dead as Terminators stuck in a burning transport, with the added bonus of freeing up Piranha usage for an extra turn.
Go and use it, though--let me know if you can pull it off with any regularity. In my experience, battlefields are seldom so perfectly aligned that it is likely to occur.