I assume you are going for a functional way to select all records (ignore the param).
I do not think you can get any default using dynamic params.
I have added '...All' records to my DB. The '...' portion forces it to be the first in the list (ascending sort) so it gets close to a default and is clearer usage than wildcards for non savvy end users. From there you just write your select statment to account for the '...All" selection option:
({?Param}='...All' or {?Param}={table.field})
Edited by DBlank - 07 Dec 2009 at 10:01am