I'm sure they could have shorten the standard time it takes under their circumstances, or maybe he could have just trained assistants. Plus, they'll have the best teacher anyone could have.
And another thing, after the Doctor obtained the mobile emitter, why didn't he use that indefinitely, and create another EMH or nurse? They were just in a shitty situation and sticking with the EMH through the long haul sounds like a risky move. If (when) he was lost, Voyager's out a doctor.