jnanian uses Caffenol-C plus a shot of Ansco 130 print developer (he said usually about 100cc or so per one-shot batch), and does a semi-stand for about 30 min.
In theory it should work with plain Caffenol plus some other developer as well. Not sure how that will behave - the vit. c tended to allow shorter dev. times than plain caffenol, but with the other developer it might mitigate the need.
Why do people insist on adding anything to coffee. Just brew up a strong pot and let it sit for a couple of hours. Then develop film in it. This is the only way I use it. Development time is long,and the negatives appear very thin, but they print beautifully.
If you do most of the resultant developer activity will be from the metol which is not what I think you really want. Ascorbic acid tablets can be found in most drugstores. Grind some up, add them to your mixture and filter to get rid of any binder.