The ice tray works well, it takes him much longer to eat because even giving smaller amounts wasn't working because he gulped it so fast. There are other home-made devices around to slow down the eating, I'll make and share more as I try them.
Surgery is not due for another month but depends on lockdown. He's 5 months but has an undescended testicle and we are waiting for him to develop a bit. The vet is open but only for emergency procedures although if his hernia acts up, she'll take him. Luckily the hernia has stayed small and we don't expect trouble from it