As someone mentioned earlier, lower the volume of the two track to record the vocals. Mix the vocals the best you can with the two track. Mix the vocal track down to two track form. Bring the two track instrumental and the two vocal up in another session. Master the vocal two track then adjust the levels of both tracks accordingly. I find that generally works well for me. I also like what someone else said by approaching the track by mastering. I actually see it that way as well. Good luck to ya and don't you love those little jobs that pay for the little things that you don't wanna put money into? lol Most money goes back into gear so it don't really seem like you're making money but when it pays for a little getaway its definitely a sweet reward.
