I agree with twiz, it won't solve the cud-spilling problem, I am afraid. But it might make him more comfortable. I wonder whether he might benefit from a sort of hybrid of TLD (twin lamb disease) drench and the drench we give them for bloat? (But probably without the oil and bicarb, unless you think the rumen has stopped processing.)
It might be worth adding some probiotic yoghurt and a bit of ginger to an electrolyte or TLD drench and see how he does. I had one calf really loved his bloat prep and would drink it out of a bucket, so you might find you can put the drench, yoghurt and ginger on some feed for him, and not have to drench him by hand, once he is used to it. But even then, I would say it would be a stop-gap, sorry.
I also agree with twiz about buying the real McCoy. TLD remedy is something you will need to have on hand for lambing anyway, so you could get a bottle and give him a dose to see. Same with PSF (Pfizer Scour Formula) or similar; something you keep by you at lambing time. (And all will have long expiry dates.)
But yes, there is a cheapo when-the-stores-are-shut version. For a sheep that's not eating : Lucozade! (The original version.) Or for one that is eating, molasses dribbled on the hay or cake.