that sounds scary, kath. i hope he's ok being home tonight. :YMHUG:
have you tried the typical anti-constipation tricks? some people have success with canned pumpkin (no spices), my vet had me give punkin oat bran or wheat bran. many people add water to the food - as muh as Trey will stand - because that helps to move things along.
if you want ideas, i'd put it in your subject line tomorrow and the people with experience in that area will come and post.