I've been thinking on this for a while, and haven't come up with a solution that I like.  I haven't had a chance to look at #22236 yet, but I suspect it will help immensely.

Also, I have a work-in-progress patch for rearranging the tkinter tests into a test.test_tkinter subpackage.  At this point, I'm not sure if that will make this issue easier or harder to resolve, but it does take care of not using test_main for the tkinter tests.  I'm hoping to have some time to get that patch into a submittable state tomorrow, then have a good look at how it, #22236, and this issue interact.  Anyone who wants a look at where I'm going with the test_tkinter subpackage before I get it submitted, it's at http://hg.python.org/sandbox/zware/log/mv_pkg_tests/ (see the changes by doing "hg diff --git -r default -r mv_pkg_tests Lib/test/test_tkinter"; there are changes to other test packages in that branch as well that are missed by specifying Lib/test/test_tkinter).