While I was poking around in the interwebs, I found this little gem:http://www.wabasoft.com/download.shtml
Look for "SH3" - if you modify it a bit, you can probably get a mini java on the Prizm! EDIT:
It also appears that it's FOSS, and so the source is here: http://www.wabasoft.com/download4.shtml
It's now much easier, although you still have source to modify, as this is still for Windows CE.
This should definitely be interesting