Say, why don't you allow the creator to sell GC provided they put as much value into the sale as they receive from the sale and then hold by the creator's funds and the buyer's funds in escrow. The creator can get their funds back when then repurchase the GC and thus destroy it. The creator profits if GC goes down relative to MC and can repurchase for less.
That might work too, if we can somehow make that more attractive than just holding MasterCoins instead . . .
It is more attractive because they get to double their gains as MC appreciates against GC. Say 1 Oz of Gold is worth 100 MC. Suppose Alice has 100 MC she could create 1 GC by selling it for 100 MC. You now have an escrow fund with 200 MC (100 from buyer, 100 from seller) that is owned by Alice and 1 GC owned by Bob. Alice is not allowed to spend the Escrow fund until she buys back the 1 GC.
If GC goes down 50% (MC doubles in value) then Alice can buy back 1 GC for 50 MC and walk away with 150 MC, a profit of 50 MC. These 50 MC are also worth 2x as much.
As long as the network forces Alice to cover her position before 1 GC is worth 150 MC then Bob has nothing to fear and can be 100% certain the GC will always be worth 1 Gold Coin.