Hi Mac
This is a great idea and I don't see why I couldn't make it work.
I can input midi thru my guitar controller and add the voice you suggest.
Taking it a step further from just a melody line, I can even do a midi track of arpeggiated guitar strings (bottom 4) at the song's chord changes. Might help by giving me more harmonic info - not too spread out - maybe eighth notes - which would make it easier to focus my pitch. The next thing is then selecting the ideal voice - nylon guitar is mellower or as you suggest a pad that will work with the eighth notes. I often reference my guitar in this way, so it should work in the midi format, and I can definitely see benefits in wav conversion and use of compression and futher eq if necessary.

Now if I can just google a headphone setup with 10-Band eqs on each stereo channel then I may have given myself a fighting chance with my current level of hearing . . . for a few more years yet.

The goal as you say is reducing the amount of pitch drift in the initial recording.
Looks like I've got a project for the weekend. . . and then some
Good stuff - thanks for the input.

Ian

Ian
My "Original Tunes" Site
My gene pool needs more chlorine.