Agree with Colin.
+ Not all fit shims/padding are created equal. I am a big fan of neoprene. You could use a full size tongue shim, laminated from the top of the tongue to the toe box. Or use the same neoprene, laminated above the toes to the top of the liner.
With overlap shells, I prefer lowering the roof with neoprene vs raising the floor with bontex. Another view, tongue shim = very elegant solution to drive the heel and foot to the back and bottom of the shell. Gives the shell back the retention power it had when it was new. Bontex or 5 iron bottom filler = taking up extra volume in a boot that is too big or wrong shape match to start. Raises the foot off the deck. Both = respected methods of reducing internal volume in a ski boot.
Neoprene is soft enough to compress, but returns to it's original shape for a very long time. Unlike most "fit aid" foam, neoprene has little compression, and very slow pack out. Sven Coomer has picked this material for the front half of all his Zip Fit liners.
IMO/JFWIW, If you can acheive control and hold down of the foot from the metetarsal heads back to the heel/ankle/instep up to the lower leg area and still have some freedom in the toebox, you are one lucky skier.