There are always those "frameless" frames - the 
ones that are basically two pieces of glass held 
together at the corners by screws. But I wouldn't 
use something like that unless you found a UV 
protective one. Getting one made specially would 
probably be prohibitively expensive. But even if 
you were to find a UV protective one, I would be 
very leery of using it simply because I'd be 
afraid the cel (paint) would stick to the glass 
behind it.

Basically, if you want to display the cel on your 
wall, the *safest* way to do so is to frame it in 
a *real* frame with acid free mats, UV protective 
glass, etc. Anything else can't be recommended.

Many Sharp Smiles,
--Drac