I have solved this problem by scheduling another mbean, which then uses JMS to kick of an ejb. this solved the problem whereby the code needs to be in lib/ext.
secondly, the scheduler (2.4.4) doesn't work very well creating multiple instances (there are other problems too). i solved this by hacking the scheduler. if you want my hacked version let me know (firstname.lastname@example.org). i can't say that all the bugs are out of it, but you can schedult multiple instances.