Hello,
What do you think about some base map pack, that would be downloaded with zero-k as game? The whole game would require 400Mb to download, and it will contain, lets say, 10 most used maps. Admins could easily find them out from replays, or simply make a vote about it. Every player, entering game would then have those 10 maps, so then they would not have to download every game they wanna play and others do not have to wait 10 minutes, they just vote some base map.