I dont know if this will pertain to your situation but if your snake is underweight...
I had a girl that would not eat for about 4 months. I was concerned because she was losing weight. She lost 100grams off her 700gram weight. I had to get her to eat to get a fecal sample for the vet to check for parasites.
I continued to offer every week a rat then after she refused a mouse. I heard that once a snake is almost done swallowing (just the tail hanging out) you can follow up with a pk/ft right after and they will continue to swallow. Well she finally took a mouse so I placed a prekilled mouse inbetween her open jaws and she took it no prob.
I guess technically this is assist feeding but it was very low stress for her as I did not have to pick her up or anything she just kept on swallowing. In the long run I got her fecal a week later and she was fine, no parasites, she as just fasting.
If your snake is losing weight and it will not eat more that one prey item this may be something to keep in mind.