stop playing, yawn, and go to the bar?
j/k... if the guitarist is good and has a big sound, you shouldn't really have to do anything different... and actually, if anything, sometimes it is most effective for the rhythm section to actually get tighter/smaller for a solo... that way you have somewhere to build with the soloist, and there is a greater potential for dynamic expression. also, if the solo sucks, you can create some excitement by developing the dynamic intensity of the rhythm section, thus creating the impression of a good solo! as a bassist, you have to make the soloist sound good, even if they aren't super great... always the challenge in that case... easy and fun with a great soloist.
john