I'm afraid you will have a hole to cover
Would you just cover it up with Sculpey?
ex. squish--> |0| <--squish!
| = Sculpey
0 = hole
The thing you have to remember is, you'll be filling a void, so you need something at the back of the ear opening to stop what ever you use to fill it, be it sculpey or other, from just falling inside the head cavity.
I little trick my dad taught me yrs ago for filling holes in cavity walls and ceilings might be useful here too.....
Get yourself a piece of stiff card, slighter bigger than the hole you wish to fill, poke a hole in the middle, and thread some strong string thru the hole, and tie it off at the BACK (very important) to a small piece of toothpick, then glue the Piece of card inside the hole you wish to fill..... , using the string to hold it in place whilst the glue sets.
Once set, you'll be left with a much smaller opening, which can be filled a lot easier, with much smaller amounts of filling. Just trim the string back to the card once it's stuck firm.