MarketPress Category page -- include other category

I am trying to setup a "generic" category, and display this on a category list page *in addition* to the current category.

I know I can do a separate loop, but I would prefer not to run through the loop twice for performance reasons.

Is there a single query that could do "current category" + "generic category". WordPress has an exclusion function, but I can't find an inclusion function at the category level.