Youch!! hope your arm gets better that looks awful.
I have a blister on my hand about the size of a £2 coin from leaning on a hot chassis tube this week, idiot! and I thought that hurt at the time but can't imagine what that felt like. I've resisted picking the blister though.
Ironically I read a post on locostbuilders last night when looking up rads about some "beading pliers" that you can get from B&Q put a nice lip on alloy/copper pipe easily.
Heres some links, think you could make these though with an old pair of pliers.
http://www.youtube.com/watch?gl=GB&h...&v=2MwmDJuOGwU
http://www.locostbuilders.co.uk/view...php?tid=116013
Chris