You can "exploit" quitting mid-match just as well, and I'm trying to avoid exactly that.
Okay, to make it less exploitable, deny it on first three turns. It's simple, but it should be enough.
Uhh, also, even if you do make a second account with a horrible deck, what exactly are the chances that it'll meet your main when looking for a match? And how often do you have to grind it just for it to give any points for defeating it?