Do you live near any other "mini people" who could baby sit him for you?
It sounds to me like his life will be a lot easier if you do make a dry lot at your place for him and that could be where he really should always have turn out.
I have a mare who foundered and it ws not a severe case apparently, however, my vet told me NO GRASS again. She is not to go out on grass ever.
Given the time of year, I really think he could be heading for really a bad situation if left out on grass for any amount of time.
As a really last choice as far as how to help him while you are gone, what about a muzzle? I assume someone's coming by to feed while you are gone? So they could unmuzzle him at feed time. The thing that worries me about muzzles is that horses CAN drink in a muzzle, but that does not mean they WILL.
Good luck.
Oh, I think you and I were typing at the same time.
I think leaving him in his stall w/ the run is a perfect solution for while you are on vacation, and then when you are back, he could go out in the dry lot where the dog will be while you're gone.
He may not like the smaller area as much, but at least he will be safe there