- Extract all the tracks to wav files using Exact Audio Copy.
- Use WinLame with Lame v3.92.
- Choose all the wav files, and use the predefined preset "alt-preset: standard + nogap"
- Run all the resulting mp3 files through vbrtagger (http://www-public.tu-bs.de:8080/~y0010858/mp3lister/) to generate a Xing header.

My results:
testing for audible transitions between two files (Jesse Colin Youngs' Lafayette Waltz -> Jambalaya)
Lame 3.92 | Win98SE | EAC wave file rips.
Anytime --nogap was used, Lame issued a message about Xing VBR headers being disabled - even when doing cbr.
Inputs using --nogap file1.wav file2.wav (single spaces between arguments)
outputs were file1.mp3 file2.mp3
All listening tests on the player.

1. lame --nogap walt.wav jam.wav
128kbps CBR. Both with or without artist/title tags, I could detect a minor (almost inaudible) blip.

2. lame --alt-preset insane --nogap walt.wav jam.wav
320kbps CBR. Same as #1.

3. lame --alt-preset 192 --nogap walt.wav jam.wav
192kbps ABR (average bit rate). Slight blip. Track time inaccurate due to missing Xing header. Adding Xing header with VBRTagger fixed track times, but made a very noticeable gap.

4. lame --alt-preset cbr 192 --nogap walt.wav jam.wav
192kbps CBR. Same as #1 and #2

5. lame --alt-preset standard --nogap walt.wav jam.wav
HQ VBR. Least noticeable blip. Usually did not notice it at all. Track times bad of course. Adding Xing header made a noticeable gap. Adding artist/title tags did not affect anything.

My conclusions;
Lame's --nogap removes Xing headers for a good reason. Adding them back in to fix the track times totally defeats the --nogap function.
While my results were best with --alt-preset standard VBR encoding*, I'm not sure that I want to live with the screwy track times.
The absence or presence of ID3v2 tags does not seem to make a difference.
That leaves using CBR. I would go with CBR in a fairly high bitrate mode, and using the --alt preset cbr xxx format in example #4.

* I was surprised by this. I had assumed from my readings on the board that VBR would cause a problem. That may still be true, but not for the sample files I worked with.