You could boost the the word count by using a hidden property like you suggest, but the effect will be limited. The EPiServer search algorithm works against you by lowering the weight (importance) of the search word as the count increases. But, even after this adjustment, it's bound to have a boosting effect :)
Full details on the weighting system here
Allan has written a post about how to "cheat the search ranking", that might help: http://labs.episerver.com/en/Blogs/Allan/Dates/112230/8/Pimp-up-your-search-II/
Frederik: Allan's method seems like a manual version of the method I had planned on. We'll give it a try and see how it works. I'll report back.
Is there any ability to bias search results? We have results coming back from a full-text search where pages that have the search term deep in a 2,000-word page body are ordered before pages where the term is directly in the PageName.
Alternately, does the system use the word count? On the tblKeywordPages table, there's a column for how many times the term appears in the page. Does the system use this to order results? If it does, I'm wondering if, on publishing, I can duplicate the PageName 4-5 times in some hidden, searchable property, therefore boosting the term's word count whenever it appears in the PageName.