TBH, I wouldn't bother. If he has plenty of forage available, he is unlikely to do himself any harm. We feed barley/oat straw to our good doers, so that they can have ad-lib forage overnight. The only time we have ever had any problem, was once when a mare decided that she didn't like the hay provided and stuffed herself with her wheat straw bed instead. She had a simple impaction colic which a vet visit soon sorted out - we changed the hay and she never did it again.
Keep the bed a tiny bit dirty - don't put fresh straw on the top of the bed but mix it in a bit with the older bedding. That's the only thing that stops mine and she'll eat anything if it stays still for long enough!
I definately recommend diluted Jeyes Fluid and spray it over the top of your bed, works wonders you only need to use it a couple of times, they soon learn
I've tried jeyes fluid but my mare still ate the whole bed literally - there was only her poo left and I don't shrimp on how much I put in! After being on shavings for years I've gone back to straw as she's retired now so her eating it is not as much of an issue. I now spray a mixture of eucalyptus and lemon grass oil shaken up with water so it goes further. It doesn't stop her completely but there is still the majority of bed left in the morning!
I had to change to shavings as even with copious quantities of Jeyes all over the straw my cob mare would eat the lot. There was literally nothing left in the morning but bare concrete! If it had just been a bit of straw I wouldn't have worried but an entire stable full every night was just an impaction colic waiting to happen!