No modded Xbox required, but i can't send a movie so i'll post it here.
I discovered this one ages ago. Basically, all you need is a plasma 'nade, and throw it at the right hand side of the hole...time it right...run...jump!
If you don't make it quickly revert and try again.
A nice trick, getting over the Keyes hole
people have done every trick, i posted not to say hey i did this first or look what i found, its more to educate others who havnt seen that trick and would like to do it themselves, just because multiple people have done a trick doesnt mean everyone has seen or heard about it, so to them it might be interesting.