Cat won't keep himself hydrated despite water fountain, S/O food, chicken broth (low sodium), etc. I don't know what else to do.

Species: Cat (Ike)

Age: 3-4

Sex/Neuter status: male, neutered

Breed: domestic (medium?) haired

Body weight:~17 (I know he is overweight)

History: Blocked twice requiring hospitalization with struvite crystals. Once February 2015 and then towards the end of 2015. Straining in the litter box last weekend, took to the vet and they did an ultrasound and said there is a lot of "grit" in his bladder. Gave him a subcutaneous hydration shot and he peed like a racehorse the rest of the day and he went back for another one the next day. He is on pain meds (liquid) and anti-spasmodic.

Clinical signs: Urination has decreased significantly and he poops maybe once a day, if that.

Duration: See above.

Your general location: NJ

He has been on the S/O wet food since February of last year. There are three other cats in the house though, so starting today we put them all on the S/O dry food (so it is the only cat food in the house) because Ike gets his wet food morning and evening but can roam the house during the day and can eat the dry food. I have a water fountain for him and started putting ice cubes of low sodium chicken stock in said fountain on advise of vet. He just really does not pee or drink much (and has a small bladder to begin with per the vet). I don't know what to do with him if he just won't keep himself hydrated. I add water to his wet food as well.

How much would a perineal urostomy even help if he just won't drink? Assuming I can spend the $3-$4K for that. His vet recommends that after two blockage (which has already happened).

Are the subcutaneous shots something I could do myself (or a family member that's a doctor) just to keep him hydrated and flushed?

Any advice is appreciated, thanks.