I've never used that Sonar program, so does it multitrack? If so, all you have to do is record your solo in a separate track and then send it. But you'll have to give me a time index so I have some idea of where to synch it up with the backing track.
Maybe we can come up with a better way of doing this, but with ACID it would be a snap. Without those sfx files synching up different files is kind of a trial and error thing.