If your sole issue is falling asleep too quickly.. try to induce SP with your forearm up in the air. Sounds a bit crazy but it's much better than the original (that being sitting in a chair holding a rock over a metal bucket). Once your forearm falls, you should awaken and raise it again. This teaches your mind how to linger at that awake/sleep state.
Wait what?
Sorry ive never heard of this technique before. Would you please be able to explain that again in greater detail? Or just attach a link to the tutorial for it or whatever.

Thanks!