Another thought I had (because I had to access it the other night) is to start slow. I know that the OP was concerned about being thrown into the pool without warning but you will get some notice usually and you should always be ready for someone to turn to you and say "go man!". My advice: try to lead in with a simple but strong statement. This can be a single note pattern or a simple figure, but play it strong, take up the space, own the attention you are now being given. And by all means stay calm. You have them, now KEEP them. Start with something simple. Then expand. Try a melody fragment and mess with it. Try a rhythmic figure and show what you can do to break up the time. In short, take them somewhere. It doesnt have to be perfect, its a solo, the audience knows that. My hero Charlie Haden often stumbled into some of his solos and then slowly wove his magic. This journey can be very rewarding for and audience to take with you. Remember, it's your solo to take and do what you want with it. I believe you can take a one, two or three note solo and make something out of it if you are communicating to the audience what you are trying to show them. Show them what you got, not what you don't got. Be yourself, solo within your abilities, and do it with spirit.