I have never found it difficult to get the exact chord I want, including Mmaj7, using slash/substitutions or the various techniques cited by Andrew and Matt Finley (particularly HERE.)

But now I realize you are trying to replicate an exact recorded track. May I suggest that if you’re trying to “get it close to the organ part in a Wes Montgomery recording” and you’re “just aiming to use it for practice,” then perhaps BIAB is not the best tool for this purpose?

Attempting to use BIAB to absolutely faithfully reproduce a commercial track note-for-note is like trying to drive in a nail with a screw-driver. It’s not the best tool for that. BIAB never promised to be a track duplicator, and jazz, in particular, is too complex harmonically for any RealStyle to perfectly replicate the recording of a particular artist.

I love it to make my own original arrangements. But if I ever needed to duplicate note-for-note a commercial track I would not use BIAB, but instead a DAW, sample libraries, my ears and, if necessary, some tools like Melodyne and RipX to isolate and duplicate something if I want it to be a note-perfect copy. RipX (also Spectralayers) can isolate instruments in a recording and make separate stems, and RipX can actually convert any separate instrument in a recording to MIDI, which could then trigger a sample. Melodyne can also identify the exact notes inside a chord, which is handy too.

Anyway, since you are just wanting to practice with the track, HERE (Play) is your track which I ran through RipX and told it to take out the guitar, which took less than 5 minutes. That’s what some people do to make practice recordings for any particular instrument. This would be faster and more accurate for your purposes. You can hear the guitar in a few places that the program did not catch, but that is easily edited too (but would have taken three or four more minutes and I just wanted to show how easy this is.)

Of course, if you wanted to replay the Organ, you could also do that, and there are a few tools that play a great sounding B3, even with automatic chords like BB, but the best is Toontrack Session Organ You could also use RipX or Melodyne to convert the isolated organ to MIDI and trigger it with the Toontrack sound. It is also possible to combine Rips of separate stems with a BIAB session, but this requires more tweaking to align the timing, but is reasoably easy too.

Don't get me wrong, I think BIAB is absolutely fantastic for making tracks to practice to. But in your case it seems you want very specific duplication of a track, so in this instance perhaps you could do it better, or quicker, with other tools.