Although you can't get the niceties of changing the divisions between the bands and interactively choosing the colors of each band, you still can create a new overlay color palette with 40 bands by creating all 256 (up from 128 in Dec.2006) entries yourself in a text file. You'll need to duplicate each color's RGB entry about 6 times and either setting the remaining 16 entries to 0 to show through, or #010101 for almost black or repeat entries from the ends. With just 40 bands, the colors will be interpolated unless you fill all 256 levels. The procedure is described here in the sections "Defining Colorbars in External Files" and "Reading Colorscales at AFNI Startup." I've attached an example screenshot using 3 color bands over all 256 entries.

[afni.nimh.nih.gov]