I don't know if it is possible as I don't know how Timer Service works internally. I guess you have tried to do this and failed?
In any event, there will be no more code changes to EJB3 until after JavaOne unless they are critical bugs.
I just commited some changes to the following EJB3 classes:
They were referencing the following classes from EJB 2, but they turned out to never be used: