How to search games by multiple concepts

For example, I tried searching by http://www.giantbomb.com/api/games/?format=json&api_key=APIKEY&concepts=3015-4, 3015-10

and I get results that don't seem to fit. I've fiddled with it as much as I can to no success. I would love to be able to get a list of games that include every concept I search with.

Any help would be GREATLY appreciated!

Thanks

Bumping this because I just started writing another function in my motley collection of PowerShell to do this exact thing.