Perhaps he's asking to do this to preview a map (maybe an aerial view of the terrain). Using a button system to select and keyboard selection system, he ultimately wants to make a map picking system. The host can possibly use left and right arrows to browse through the available maps.
Examples of a keyboard system is "Impossible Bosses". Players use left and right arrows to preview certain units. A very close eye level camera shot is taken of each unit. I think a game called "Pimp Hero Defence" (If anybody played that, haha), somehow displayed an image of a prostitute on the screen if you win the game (LOL....). So such a system must be possible.
However, I'm just guessing what he wants based of what he's told me.
Edit: If you can't use a button system (like a lot of SC2 maps seem to feature, perhaps you can use a command system. Where "-select" picks the currently viewed map?