Is there any way to use the piano roll editor to enter (or properly quantize) 3 quarter notes spread over two beats in 4/4 meter (as in "April in Paris" melody)? I've tried playing it in but can't seem to get the right "feel".

I found how to do it. Not in the piano roll but rather in the notation window. I just left it in 4/4 meter then in "Notation Window Options" selected "3 (triplets)" in the Resolutions options. At that point I could see there were 3 subdivisions per beat on the grid in the notation editor. I placed my quarter notes at beat 1 subdivision 1, beat 1 subdivision 3, beat 2 subdivision 2. PTPA distributed the quarter note triplet evenly across two beats as desired and play-back sounds as it should.
DVJ

Glad you were able to figure it out!