I went to a bar a few years ago and there was someone set up at a table in the corner with a weird-looking deck of cards and a sign that said, "help me test my game design!" That particular approach worked really well, but I think particularly because playing a game in a bar is fun.
In this case, it might work because you're not only asking for feedback; you're also (hopefully) contributing to people having fun.
$10 if you give me your opinion about my idea...