[xmonad] fuzzy/partial matching on prompts?

I haven't been able to find anything in the docs on this… All I want is for certain prompts to use fuzzy or partial matching: the XMondad.Topic switchTopic function was what prompted this, but I see plenty of cases (dzen) where it would be very nice. But particularly for switching topic/workspaces: it's a pain having to type out whole names, even when the list has already been narrowed to a single member… There's probably some configuration option I'm missing—does anyone have any pointers? Thanks, Eric