I really think that will help- he just doesn't need that much food. A larger breeding female would eat mediums, but most people have the best luck keeping male BPs on small rats.
As far as using the hairdryer, use that briefly just before offering the prey- it should be fully thawed & warmed first, but the extra blast from a blow dryer just helps many BPs to target their prey, since they rely so much on their heat-sensing pits. Probably worth a try, since even fully-warmed prey cools off so quickly.
By the way, if you already have some medium rats on hand & nothing else to feed them to, you don't have to throw them out either. I'd just wait 3 weeks to offer his next meal- it won't hurt anything & you might see a better appetite. If so, that will help confirm that small rats are the best size to feed him.