Hi Steve,
Unfortunately there isn't a way this can be done without heavy modification of the current code. The multi search is really an experimental feature, and we're hoping to upgrade it soon.
You should find that search engines won't index links from the search page results, as the only way that links from it would be displayed is if a search was carried out first, and although bots will follow links on the page, they will not submit forms.
Thanks!
Greg
Greg Thomas
PHP Programmer - interactivetools.com