hey mat i did mine yesterday, the TF is slightly different as it's a 6 bolt not 4, but i was pretty lucky in that they didn't round off
i know what you mean about inaccessibility though the subframe really gets in the way
I did it by putting the socket on the bolt and then putting on a 90 degree flexible thingy... not sure how to explain it better than that, its a pice of a socket kit that can turn, and twist... i put a 12" extension bar on the end of that and it went past the subframe easily enough, but they dont help with the rounding!
the other option would be to unbolt the manifold and the flexi from the cat...
you could then hopefully pull it down far enough to get at the nuts better (that sounds so wrong)
the last and most drastic would be to turn the engine on and VEEEERY Carfully crawl under the car and hope the heat of the exhaust gasses will loosen them off, god help you doing this though i hope you dont like your skin!
thats all the ideas i have so far? hope it helps