Advanced search - search manufacturers without keywords

I know this has been asked before, but I need to modify the advanced search module so that it works when only the manufacturer is selected. At present, it only works if a keyword or price range is entered along with the manufacturer. Can someone please come up with code changes to perform this function or at least point me in the right direction. I'm using a modified advanced search sidebox which you can view at http://sydneyautos.com.au

May be the topic below is discussing the same issue.
Search Without Keyword

And v1.3.5 have the function built in.

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Thanks, but there is still no solution in that thread. I need the advanced search to work when only a manufacturer is selected and no other fields are filled in.

Using the Manufacturer's Sidebox is not an option for that?

No, I only want to have the one search sidebox. I like the look of the sidebox the way it is but it confuses customers when they select the manufacturer, click search and get an error message.