How do I register a custom runner for Test::Unit?

[Eric Promislow]

Three years ago in http://tinyurl.com/2xkvrl
(http://groups.google.com/group/comp.lang.ruby/browse_frm/thread/
5df4ed2c27d59326/d69077b7759fe4bf?hl=en&lnk=st&q=ruby+test+custom
+runner+group%3Acomp.lang.ruby#d69077b7759fe4bf)
someone asked Nathaniel how he could register his custom test runner
without hacking the list of RUNNERS in test/unit/autorunner.rb

Nathaniel's answer was to use an explicit call, as in:

MyRunner.run(MySuite)

This still seems to be the case. I would like to invoke rake with the
TESTOPTS env var pointing to my custom runner. Is there a way to get
around both having my customers manually hack autorunner.rb (or
supplying them with a script to do that, which is probably no better),
while still using Rake's ability to discover the tests, build the test
suite, fire the runner, and return the results?

I'm trying to avoid reinventing as many wheels as possible here.

Thanks,
Eric Promislow