I did understood you question. You asked for the right formula. I figured out you already knew how to load data from a URL and you had problems making out the correct URL. My answer was supposed to suggest that you need to concatenate the URL to the short/full address.
BTW, my solution is:
=importdata(concat($A$1;B2))
A1="
http://btc.to/", A2 and down has the formula and in column B I write the addresses.