[plt-scheme] Multi-column list box control?

Hi,

Back in 2003, Rian Douglas asked whether any work had been done
on a multi-column list box for the GUI library:

http://www.cs.brown.edu/pipermail/plt-scheme/2003-July/003251.html

I'm in need of one for a database application, and, no, arranging  
multiple
list boxes side-by-side won't suffice.

Of course, I'm quite willing to hack one myself.  However, being a  
hack for
myself, it likely wouldn't be fit for public consumption, and I  
wouldn't want to
have to maintain it under the mred collection directory in the face of  
PLT
updates on my various computers.  Given that, has anyone any advice on
how to pull the various private mred bits (kernel.ss, etc.) into a  
separate
library directory structure.  Or, would this be as much trouble  
maintenance-
wise?

Thanks,

Mike