Instead of crating him, why don't you securely baby gate him in an area such as a kitchen or bedroom (Do not close the door) leave, his bed, tv or radio on, lights (Since you are away so long it could get dark) a stuffed frozen kong, and several toys. A nylabone or a none ingestible bone so he can chew is good too. (you don't want to leave him with anything he can choke on)
It's not working in the crate- time to try something else.
I'd still look into a dog walker. When they are racing, they are let out 4-5 times a day for an hour each time.
Just because he can hold it that long, doesn't mean he should have to. That is unfair.