That doesn't sound right, though I have no science to back that up.
Seems that absorption would be fairly consistent since there is no way for the snake to know if it would be eating weekly or monthly or whatever.
An interesting question which has been discussed before.
I think if you actually mean how many grams of a 50 gram rat becomes snake and how much snake poop, I think the answer would be fairly consistent whether feedings were regular or not.
I'd like to know the answer myself, since I'm just speculating.