I bin most of my sheds. I've given a few sheds to friend's kids. I currently have one particularly good shed (all in one piece, nice and flat) hanging next to the vivs.

I think that once the shed has dried you would be very lucky to flatten it without tearing the shed. The best bet is to catch the shed while it's is still moist and lay it flat and stretch it out while still moist. I guess there may be people on the forum who haven't picked up a shed immediately after the snake has "vacated" it, who may be surprised to know that sheds are very moist and flexible, however they start drying at the head end even before the snake has finished getting it's tail out.