http://bugs.winehq.org/show_bug.cgi?id=34959
--- Comment #1 from Ken Thomases ken@codeweavers.com 2013-11-20 12:06:26 CST --- I posted a request for a suitable icon to wine-devel in October: http://www.winehq.org/pipermail/wine-devel/2013-October/101598.html
If and when we get one, we can bake it into the Mac driver and use it when the executable doesn't have an icon. To change it, you would have to patch and build a custom Wine. It wouldn't be runtime-configurable, at least not given how I plan to implement it.