Is he actually losing weight?
This time of year, many male corn snakes do go off their food - they're more interested in breeding than in eating.
I wouldn't try feeding more than once a week, and if he refuses, leave it overnight. If he won't eat, weigh him again.
"My bum has been a bum for a very long time, but that does n't mean I have to listen to what it says."
- Terry Pratchett, Fifth Elephant