Auto-complete for multi-valued cells?

Hi --

I'm trying to build a spreadsheet that allows users to enter a comma-
delimited list of values in specific cells, sort of like a list of
tags in delicious etc. The values should be from a restricted list.
For example, if the restriction is a list of names of fruit, it would
allow users to enter "apple, banana, pear" into a cell.

To help users enter the correct values, I would like to show an auto-
completion menu while they type. Excel's autocomplete works for a
single value match -- in the above example, it would match "apple".
But once you've 'accepted' the first value by typing a comma, it will
no longer match as you start typing the first few characters of the
next value (banana).

Is there a way to subvert the built-in functionality to match
individually in a comma-delimited list? And if not, is there a way to
reproduce this functionality from within VBA (e.g. trap key-presses
and do the completion match yourself)?

Thanks!

Ramon