Whoosh!, I did this last night, re-setting an old Raleigh 531c frame from 123.5mm (?) to about 130mm for a 9-spd freehub. As Hocam suggests, I did this at my local 'bike church'. http://www.thebikestation.org.uk Despite spending 20 minutes searching skips in the locale, in the snow, for a suitable bit of timber to use as a lever, I managed to successfully set the frame (is this 'cold setting' ?) then realign the dropouts afterwards (with the right tool). It took me ages, because I was terrified of bending the frame too far (as it is, I had to correct my adjustment by about 1mm) but it seems to have worked ok.
Bear in mind, though, that the mechanics at the B.C. will probably be briefed on a principle of 'first, do no harm' so don't be surprised if they advise against you doing this! I volunteer at the place mentioned above every week, and I was firmly discouraged!