Is there any way to customise sorting of directories in the index?

[Chris Green]

I have a about 40 or so folders where I save mails I want to keep,
with names such as 'shopping', 'motorcycle' and so on.  By default
these are sorted alphabetically in the index which is not ideal.  I
save things in 'shopping' far more frequently than elsewhere so it
would be really handy if that was at the top or at least near the top. 

Is there any way to customise the sort order?  I suppose the ideal
would be 'most recently used' at the top but even reverse alphabetical
would improve things.

I *could* rename 'shopping' to 'Shopping' to fix that one but I'd
really like a more generally applicable solution.

-- 
Chris Green