marketspreads.ie have some Euribor interest rate futures that you might be able to use, and I'm sure other spread betting companies do too. This is something I am currently looking at as well.
Note: I have no affiliation with marketspreads other than being a customer.
It would have to be something that you could keep rolling over indefinitely for a minimal cost.
I would have thought one of the spread bet companies would track the ECB rates.
You should find them on most financial spread betting sites.
But I cant find a product that would suit. You can get Euribor to Dec 2011, but what you need is ECB to the end of your mortgage term, or at least a cheap rollover.
The best way is financial spreadbetting, so you can gear up. Otherwise you'll have to invest the same amount invested thats outstanding on your mortgage. Sure then you might as well just pay off your mortgage with it.
In a nutshell.
For the cost of rolling over (which should be small). You bet enough on the ECB rate increasing. to cover what the extra cost on your mortgage would be.
The idea being that if the ECB rate increases you win the amount your mortgage is going up by.
But if the ECB rate goes down you lose the amount you would save on your mortgage.
So it all more or less balances out. You dont care whether you win or lose, because you should always be up by more or less the same as you are down on the other side of the equation.
Maybe ring the spread companies and ask them if they have such a product. Im sure they do. The demand would be massive.