The resurrection of this topic reminded me finally to do something after, once again, a total loss of the rear brake at an inconvenient moment.
I went for KZMille's two-position technique described in the Aprilaforum link. Actually, I bled the brakes in both positions more than once, just to be sure. I also tied the caliper up as high as possible, just under/by the rear frame tube (the plastic in-fill piece under the seat had already been removed for repair, which helped). This results in the brake hose rising directly from the cylinder and having no possibility of trapped air (unlike Carnivore's technique - see photo above). I used the thick flat of a large open-ended spanner to keep the pads from closing and secured that in the calliper with more string.
Seeing as the brake fluid was supposed to have been changed in the major service I forked out for last year, I was not impressed to have to top up the reservoir three times (it may even have been four) before the brake pedal firmed up, then a final top-up. On the other hand, it was rewarding to see so much air coming out. I'm amazed that the brake worked at all.
BTW, that little black rubbery bellows thingy just underneath the reservoir cap threw me at first, until I realised it was just a kind of protective cover. Well, I assume that's all it is. You do have a little black rubbery bellows thingy, don't you?
Having read KZMille's explanation for the two-position technique in the Aprilaforum, I cannot be sure that Carnivore's single position is adequate. Just saying.
Anyway, the brake feels really solid now. Definitely worth doing.