I watched Bob Shane break a G string, continue singing and reach into his pocket for a string and a winder- then change and tune up in time to be playing at the last verse. Utterly amazing- of course, 45 years of practice probably helped. The winder was obviously the key to the whole process going so quickly. If you don't have a group to sing along with, maybe just a little casual banter with the audience would work- string changing shouldn't require such great concentration.