How to prevent reinstalling software with user based deployment?

I've just discovered user based software deployment and it works great.

I wanted to figure out a way to limit the software installs to machines that don't already have it installed.

With computer based deployment this is easy. I just create a collection query that looks for an entry in add remove programs or looks for the presence of an executable and make that a sub selected query for workstations that are not in the sub query.

But how do you do that when your targeting users or groups instead of workstations?