One, this might not be a problem at all. Especially an adult male will fast for a LONG time. I have a male that maybe eats six times a year and seems very happy for it. Other breeders/keepers will tell you the same thing. Is he losing condition? Does there something about his appearance or health that makes you concerned?
Two, in addition to changing around food items to get his interest, you could try altering his environment. What is it set up to be now?
You could try putting him through a good cold spell, increase his hot spot during the day, fluctuate the humidity a bit, do a full cage clean out, etc. Whatever you try, be gentle, but sometimes a snake just needs a change of scenery to get the juices flowing again.
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26 year old 0.1 from Lincoln, NE
Ball Pythons - 0.1 Silver Bullet, 0.1 Pastel, 1.0 Pastel het Pied, 0.1 Pied, 0.1 Cinn, 1.0 Black Pewter, 1.0 Woma, 0.1 Yellowbelly, 2.1 Normals
Kingsnakes - 1.0 L. m. thayeri, 0.1 L. m. thayeri X L. alterna, 1.0 L. g. californiae
Other - 0.1 Whitesided P. catenifer sayi, 1.0 H. nascicus, ?.? Chrysemys picta, 1.0 husband, ?.? Mini-human