Working with 12 edo musicians

Part 1: A friend of mine wants me to play bass with his guitar and vocals live on stage. He only plays in 12 edo and doesn't use barre chords. I've been playing 12 edo bass lines, but I wondered if I could sneak in a few extra notes. The obvious suggestions are 24 edo, or 12 edo with an extra note added a certain amount below each 12 edo note, for example adding notes about 33 cents below 12 edo notes would allow 7/6 just intervals. Could anyone suggest tunings that I could use (of the form 12 edo plus extra notes) that might be particularly effective or fun?

Part 2: He has also said that he would like to play guitar with some of my songs. I usually play guitar and sing and I don't use 12 edo if I can avoid it (I like 12 edo, but everyone else where I play usually uses it and I like variety). Should I try to persuade him to play a non 12 edo guitar (I would have to built it myself, but that's not a problem)? Bearing in mind that he doesn't use barre chords, which tunings should I suggest he plays in? I think he'd probably find pythagorean intonation easiest (It was the first non 12 edo tuning I used because I found it easier to play than most others and I didn't have to recomposed my songs), but are there other tunings that might be suitable for a musician used to 12 edo?
On stage I usually perform in Pythagorean intonation, quarter comma meantone, 7 edo or 14 edo, but I think I should extend my range. I use these tunings partly because I find them easy and partly because they have been well received by audiences (I usually play to people used to 12 edo).

> Part 1

Hi Mark. I've been experimenting with microtonal tunings for conventionally fretted guitars, by restringing with doubled strings and tuning up one of each pair by 14, 31, 50, 69 or 86 cents to allow 24EDO or simple Just Intonation scales to be played.

I go into detail in this thread:
http://www.notonlymusic.com/board/viewtopic.php?f=23&t=527

For example restringing a conventionally fretted bass with identical pairs of strings, with a fifth between the pairs:

High
D +69 cents
D
G +69 cents
G
Low

The offset strings can be tuned using the 7th harmonic.

This gives you 24 notes per octave: 12EDO plus another 12 chromatic notes offset by 69 cents, approximating these Just intervals to within 4 cents:

14/9 765c
7/6 267c
7/4 969c
21/16 471c
63/32 1173c

This method reduces the range of the bass, so another possibility is restringing with an octave between the pairs:

High
G2 +69c
G2
G1 +69c
G1
Low

No one would even know since you can use a normal 12EDO bass.

By the way, I like your music and videos.

Mat Cooper.