In fast money maps, it's not one mineral patch accumulating quickly; it's a lot of mineral patches stacked on top of eachother in the same spot. Get StarForge, and then you'll be able to place minerals on top one another. Simply place the mineral patch in the exact same place a few hundred times, or however many mineral patches you want at that location.
I believe there's another program which does this as well, and an easier method (like putting in a number for the quantity you want, and having them auto-stacked for you), but I've never cared much for making fast money maps, so I'm not completely learned on the subject.
If no one else has given you an alternate method by the time I check back later, I'll look into it. In the meantime, StarForge will work just fine.