To your original question, after I assist feed the first time, I continue until they eat on their own. In other words, I work it like this (after the first assist feed)
1) Offer appropriately sized rat and leave in for 1 hour. If not eaten:
2) Offer hopper mouse the next day for 1 hour. If not eaten
3) Immediately assist feed (read as push mouse into throat with back legs hanging out of mouth).
4) Repeat the above process every 7 days until they begin eating.
I have never had to assist more than 8 times (only one went that long, the rest of the time 5 assists has been the most).
Remain diligent, and your efforts will be rewarded.
Hope that helps and good luck,