Well I just read a thread below that countradicts what I am about to
say.  Especially considering that your kitty has been experiencing
blockages you probably want to check with your vet before trying this.

I have saved dying kitties by feeding them tuna or tuna water.
Another possibility is simply to give him some omega 3 supplements
which are rich nutrients.

Good luck. Sounds like your little guy is in some pain right now. I
know how tough it is to cope with sick kitties.  I have 1 with a bad
case of spreading cancer right now.

Amber

I also should have mentioned Science Diet A/D in a can.  You have to
get this from a vet by prescription.  When I use to work for the vet I
use to have to feed critically ill animals with canned A/D.  It is
really rich & cats tend to love it.  I think Science Diet packages
this stuck for dogs, but my vet used it with critically ill kitties as
well.  I have some here now for my Winnie who has cancer that's
spreading.

Amber