If you could find a decent teacher that knows the upright, chances are they would help you with the fretless.
One thing I learned from my studies on upright that may help you I call finger substitution. If you wanted to play in the next octave, you can put your index finger where your pinky was or the reverse. The hand seems wired to make this move easily.
Another thing is with a simple octave held by your fingers, you are measuring the neck/scale at any given position. It's easy to hear an octave obviously, but this tells you what a whole step needs to be at that point.
Of course what Gard has to say above makes a lot of sense as well. Also playing against the fifth, a third, fourth and other intervals besides the tonic as the drone helps too. Try the same thing as he said except with the A note as the drone, still playing the D major scale
works for me anyway.
jc
[Edited by Rockinjc on 08-21-2000 at 11:22 AM]