This should be a good short-term hedge against rising 30-year mortgage rates while shopping for a house. If you can afford a small swing, but if there's >1/2% rise in mortgage rates, you can recoup some of the added expense.
To keep the cost of the hedge down, you should be able to buy far out-of-the-money puts on IEF. Doing so in an IRA account will avoid taxes on the gains. If interest rates rise significantly and you sell the contract before expiration at the time you lock the mortgage, you should end up with a lump sum gain in your IRA. Then just consider your additional mortgage payments as taking the place of what would have been IRA/401k contributions.
The way I look at it is that the amount "out of the money" will act as a deductible on a mortgage rate insurance policy, and the cost per contract is essentially the insurance premium. Just buy the number of contracts appropriate to cover what you believe is a good representation the mortgage rate risk, factoring in how long you expect to stay in the house.
The relationship between the 10-year treasury and 30-year fixed mortgage rates is well described in this New York Times article.
Regarding the correlation between IEF and 10-year treasury index:
The correlation coefficient between the 10-year treasury and IEF has almost always been -0.99, which looks like a darn good security to buy options to hedge against the 10-year treasury rates changing. See the correlation plot below: