I looked it up and tried it for the first time on some Giant MPHs I'd got on a second hand bike. It was pretty easy, but it turned out there was a different problem with the piston in the lever. I got the parts for that and had a go. No joy.
At that point I thought I'd spend some money to save myself the hassle. I was also hoping to lend the bike to a friend that weekend. I took it to Evans, who made me stand around for 20 minutes, booked it in, then came back upstairs to say "We haven't got the tools to do it." I left.
I think they were going to charge £35 + parts to do it, so I thought sod that, and bought a whole new set of fully bled brakes for less than that on ebay. Now I have working brakes, and almost a whole set of spares, with no bike shop grief, and no feeling that I've been done by anyone.
I guess their £35+ charge will be swallowed by customers who see no alternative (or aren't as stingy as me).