Well, it turns out that wine doesn't respect the Windows CreateFile() flags FILE_FLAG_NO_BUFFERING or FILE_FLAG_WRITE_THROUGH. I have a really simple wine patch to "fix" that. I really haven't thought it through in too much detail, but it seems to work.
Basically, whenever wine sees either of those two flags, it just disables all of Linux's filesystem caching with the open() flag O_DIRECT. You can apply the patch to the latest version of wine out of its git repository. and probably earlier versions, too. Here's my patch.
I'll probably be trying to get this into the upstream wine distribution soon.
BTW, if you want some help building wine, I'd be happy to help, so just email me.