I know it sounds like a bit of a faff, but could you try hand feeding him individual strands of hay, maybe mixing it up with 1 blade of grass and 1 or 2 strands of hay in your fingers at once?
I'm guessing soft poops with grass is better than not eating for his teeth and digestive system?
@furryfriends (TEAS)
All of mine have hated CC, I've only ever had success with Supreme Recovery Plus.
I have a couple of old sachets here, (think they're past the best before date, but still fibre) I could send to you if any help.
Get admins to send me your address if u'd like to try them?
C'mon Pebble we're all here with fingers & paws crossed with a truckload of healing vibes coming your way too.

Look after yourself too Emma xx