Changing the sort order of a grouped lists (to a custom non A-Z / Z-A order)

Hi,

I have a list with a category field, which I am using to group the lists (so i have the nice little collapse-able groups) say:
cat:A
cat:B
cat:C

But what I would like to be able to do is change the order of this grouping to non z-a/a-z, say:
cat:B
cat:C
cat:A

This MUST be possible, but I just can't find out how :(

Regards
C.J.Murray