Well, another week and another failure, so I guess it's time to air out my frustrations and regroup again, lol. This time Iggy actually grabbed the rat by the head when he wrapped it (promising!), and then pulled it back into his hide with him after he uncoiled (also promising!). Unfortunately, that's where the good news ends, because I then found him just using the rat as a pillow when I checked on him inside his hide a few hours later. Further offers were unsuccessful, including attempts with the hot water dip.
On the plus side, when I plopped him on the scale earlier this week, he had still gained a small amount of weight - 205g compared to 194g from one month ago - so that's something, at least.