Background:
I have mortgage loan on an appartment building. The interest rate is
at prime minus one half percent (floating).
At the current monthly payment, the loan is repaid in 17 years.
 
To lock in a fixed interest rate, the lender is pricing in a premium
that is too rich, I think.
I accept that there is no such thing as a perfect hedge but I think
there must be an ETF (exchange traded fund), the price of which moves
so that if I am long the ETF, I offset my exposure to rises in long
term interest rates in the USA.
I know I can short US treasure futures contract(s) to accomplish the
hedge. However, I prefer to be long a position rather than to be short
a position. I prefer to use my regular stoce brokerage account so I do
not have to open a futures account.
What are my best posible solutions?

One way to do this would be to invest any extra cash you have in
mutual funds with most of their assets in loans.  This way you'd be on
the other side of the loan, exactly the opposite of what you are now.
I did a search in yahoo and some possibilities came up:
http://finance.yahoo.com/l?s=interest+rate&t=M

Another thing you can do is purchase an inflation-indexed security. 
The US treasury offers these bonds to adjust for CPI(consumer price
index) changes.  Basically if there is high inflation (which leads to
high interest rates) these bonds will increase their coupons according
to the CPI.

One thing worth mentioning as well is that the returns on these two
items are typically very low, but they are very safe bets.

Also typically energy and utilities do well in high inflation, as do
real estate stocks.  Just make sure if you pick one of these the
company does not have a lot of debt or they will have the same
potential problem as you!

hope this helps!