The ECU arrived today. Rushed home from work (as much as the weather would allow - an 850/1100 screen isn't quite as effective in a downpour as an Adventure one....I might as well have been swimming), whipped the tank off the 1150 and switched the ECU over. Put it back together and.......it wouldn't run. Yup - throttle cable out of its seat
Anyway, I went out for around 20 miles, still in torrential rain, and it's like a different bike. Smooth, progressive throttle response and no lurching at all. If I was being picky (and I am, generally) there is a little bit of surging around 3k rpm but it's the "they all do that, Sir" surging, not the awful lurch/misfire that I had before and the bike has the cat fitted at the moment and I haven't tried different CCP jumpers yet so I reckon putting the y-piece back on and trying jumpers will sort that.
So subject to more road testing early indications are that mine's sorted too

Scuba-Sparky, you may want to invest in a second hand ECU.
So what's the conclusion - bad batch of ECUs in 2002 or something else on the bike that messes up the ECU? To be honest, though, I don't care - after 6 months I've got a bike that runs (almost) right and now I'm just going to enjoy it. But for anyone reading this in the future, if you have a 2002 bike that doesn't run right and can't be sorted with careful setup, try a different ECU.