OK, I've looked into this some more. Ordinarily the remote will repeat without interruption for many seconds. However, assigning an EFC to a button seems to cause repeats, and unfortunately I don't see a way to send discrete On without breaks except by using a JP1.3 flash cable to load in an upgrade.

Of course, I can't be sure that even an uninterrupted stream of iR will work for you. A USB based cable cost $29, and it is trivial to use RemoteMaster to upload the upgrade.