I've just managed to get the result I was looking for, thanks to your help!

I was surprised to see that the solo is generated for the whole song, but is only played for the custom set of bars - it makes it hard to work out what's going on when what you see ISN'T what you get!

I find the existence of multiple incompletely overlapping ways of doing the same task a frustrating part of BIAB, but I suppose it's all related to the long evolution of this product and the need to keep the old method of doing things while introducing new ones to cope with features such as RealTracks.