I will warn you...if you do try to assist feed...and I am not so sure at this point it is necessary since you said he may not actually be losing weight...
But..if you do it just keep in mind that if your snake does latch onto the prey he will probably try to constrict it...and it will startle you. Don't drop your snake! Make sure you aren't far from a secure surface so you can put him down without harming him.
Alright, I'll keep that in mind. I would assume that with an assist feed there is the chance of a regurge. Of course I probably will talk to my vet before I even think of doing it.