I wouldn't bother turning a flat ruststone into the ice LS because that branch has a weapon you can make (the icesteel blade).
If you're doing daimyo lance training, you should try to get in some attacks in between his attacks. The easiest way to do this is block his attack, counter attack, and guard his next attack. You should be able to stun him before your stamina is gone.
If your stamina is almost gone, you should sheathe your weapon and retreat at the first opportunity to do so, even if he's lying on the ground and looking like an easy target.
I decided to try the training just now and the only part that might be tricky is sharpening your weapon, which you won't have to do more than once. You could probably save your shock trap for that. You shouldn't even have to worry about using your stamina up since he will get stunned often enough to recover most of your stamina.
As long as you keep counter attacking, you'll recover stamina.