The force of life is weaker, but even if it worked the way you think it does it wouldn't matter. If you have a weak body so you can't stab yourself as hard as a strong guy, your weak body will still die from the weak stab.

Unless you're some sort of god-surpassing genius, no. Something like that would flip magus society on its head. Even Touko, the girl who does that on a weekly basis, can't do that.

[quote]EDIT: Also you're leaving out the part where there's a readily available procedure to make the guy's liver work for you.[/quote]

There isn't that sort of procedure for Circuits.