you need more practice. one legged drills are tough to do on anything except a spinbike with a monster fixed flywheel. on a trainer you have to be really good. that means, keep clanking away and blowing your legs up.
increase your one legged cadence.
127.0.0.1 here can do over 160rpm for 30 seconds on each leg, it has to
be smooth, and it kinda smooths itself out the faster you go. I do want to commit suicide
in the middle of it though, maximum agony, and the fear that my resting leg will
somehow get sucked into my wheel. there is no -good- way to park your unused leg, so
I let it hang... that is hard in itself.