A sheepshank doesn't need a free end to tie - that's one of its positive features.

You're right about the other aspects, though.

(Being a climber and caver doesn't help much - most of the time, I want knots at the ends of the rope, with a nice, free-running middle part. The exceptions being adding knots to handlines - normally overhand loops or alpine butterfly knots, but you said you didn't want a loop).

/me thinks laterally...

Tie any knot that has a loop. Then simply cut the loop open. Or did you want to be able to undo your work?

Can you explain exactly why you don't want a loop? Without cutting the rope, it's impossible to avoid a loop of some sort; if we knew why it is important, there might be a possible compromise.