If the leader has used both ends and they are therefore above you, a double rethreaded figure of eight direct to the harness is easier to untie than an overhand knot
... and a bowline on the bight even easier to untie, so that's what I would use on the very rare occasion I find myself in that situation. If I don't have enough tails to tie a proper stopper I'll clip the loop end into my belay loop, but usually it's fine.
If you have to tie in the middle and don't have a spare screw gate make the bight really big (>2m) and the knot really loose (overhand is best for this). Then larksfoot yourself to the bight by putting it though your belay loop and passing the loop over your body. Then adjust the knot to get the size of bight you need.
If you're going to step through a bight and re-adjust anyway, it's just as easy to tie into a bowline on the bight. Clean, simple, bomber. The only downside is the need to step through a 'skipping rope' bight.
