Careful with the sponge idea-- they breed bacteria very quickly... Sphagnum moss is a better and safer trick!!
Pre-scenting allows the snake to realize that there is prey around and gives the snake time to get prepared and into the hunt mode. Feeding responses are usually better after pre-scenting.
I pre-scent for about an hour or so (actually, I thaw all of the rodents in the room that the snakes are in and so it is pre-scenting at various levels throughout the day.) For the snake who eats live, I prescent for about an hour and then put the mouse into her tub and walk away. BAM!!!! Job is done. I feed at night (when the snakes are active) and then I leave the snakes alone for two days while they happily digest!!
Just a thought: I leave my snakes alone for 48 hours based on their tub or cage temps and the amount of prey I have given. If temps were cooler, digestion would be slower, and I'd leave them alone longer.....