Roy Hayun presented his "JRuby on ME" talk this past JavaOne and got a pretty solid response. He ported a pre-1.0 JRuby to CDC by incrementally stripping out libraries and functionality that couldn't be supported. He succeeded, and yesterday delivered to us a buildable version of his JRubME 0.1 (that name was a typo on his original JavaOne submission...but the missing 'y' produced a comically good name).
In the JRuby download "research" area, you can find the results of his work plus some docs and a short presentation on JRubyME. As near as I can tell he based it on JRuby 0.9.8. The same work could probably be done to produce a stripped version of current JRuby, and with a bit more work we could probably tweak and reconfigure the source to support ME execution as a normal build target. Both are exercises for you all until there's more time (or Ruby on ME becomes a primary goal rather than performance and compatibility on SE :) )
There you go! You wanted JRuby on ME, now you have a damn good start! Run with it!