Well, the vet should be pretty sure if it's laminitis, that's just the inflammation part. Founder is when the rotation occurs, and that's probably what he's not sure about. You can have inflammation without significant rotation. Since he reared up over picking up his foot, I'd say that's a pretty good indicator of pain!
You're probably better off then keeping him up with no grass if you think it was a food issue. But TRY to get those pads on him. Just cut out a round 4 by 4 inches (two rounds, actually. LOL) and square off the end of one (that will be what goes across behind the toe area). This will sound hokey, but try it. First, get him out of the sawdust, if you can, so your tape doesn't get covered in it.
Fold some tape over on one of the rounds, so it's sticky on both sides. Then whichever foot is most "owey" try to pick THAT one up. If you get it up, just for a second, slap that sticky round on his sole, don't worry about accuracy! Let him have his foot back. Then see if he'll stand still and let you pick up the other foot. If he will, this one you don't have to double side tape , just place it where it needs to be and swoop swoop with vet wrap to hold it temporarily. (have you ever wrapped a foot before with guaze and vetwrap?) same method for securing this pad) . Let him rest.
You can either go ahead and work on the other foot now, and get the pad in it's proper place and temporarily secure it or continue on the same foot. Just let him have frequent breaks. Now you tape the crap out of it. The vetwrap can used underneath in a thin layer so the tape won't stick to him. That's all it's for, really. The duct tape does the holding and protecting. This won't hold for long if he gets really active or if it gets wet, just put them back on if they come off. Its' a temporary comfort measure, not permanant.
Key points: 1. Let him have his feet back as often as needed, even if it means you pick them up 100 times to get it all done. Switching sides helps.
2. The pad should be just beind the white line at the toe, so the toe isnt' bearing full weigth, the sole and rest of the foot is.
if he's comfy enough to move witht he pads on, and you can't turn him out in the pasture, try to let him in an arena or round pen for a little while (if there's minimum grass, of course). Could even try handwalking him some on dirt/grass. Let him go slow and try to keep turns wide and slow. You may have to readjust the pads after.
I wish I COULD come help!!!