A Stable Bitcoin Exchange Service

For me it seems that there are 2 things mixed.

The exchange-rate: bitcoin and other currencies
Every company which does international business copes with it.
One strategy is to handle the risks, with reserves, so changes can't harm.
The other one is to hedge it. Like airlines: They are buying futures for oil. So they fix the price of the product for several month. They are not fixing the price for the money they are using.

Customers cannot handle the risks. So they decide to buy in the other currency, or not.
As customer you normally not notice the exchange-rates. You are using euros, and thats it.

Even if the merchant fixes/hedges the prices, the price for the customers changes.
The best practice for the merchant is to track the price. The costumers buy bitcoins for a given price and pay the product.
If the merchant is able to buy his products in bitcoins too, he will use them, because then he doesn't take exchange-rate-risk
Insuring/Backing up the value of bitcoins
The question is: What happens, if the coins loose their value?

When you don't want to loose all the value then: Sign an insurance! Options/Futures are normally for the buyer of products.

The suggested exchange is an insurance, which secures a given price for an amount of bitcoins.
Nearly the same was already suggested.

One thing to take care about:
The customers only will sign insurances, when the situation is insecure. So it's quite difficult to take the risk for this short time.

I would suggest:
You pay an amount: for example 10Euros to secure 10 bitcoins for 1euro, in the first year 2 bitcoins are secured, in the following 4 ...
After some years all 10 bitcoins are secured.

If there is money left in the case of a melt-down: the rest is shared with all customers.