I've never added a lift-out, but it seems to me you could just add a cleat (outlined in Red) to the underside where the Lt Green lift-out meets the Green/Yellow main bench work. In your photo, there appears to be about 1.5" of door jam between the edge of the benchwork and the actual door with the new plywood lift-out. If you replace the 10" track with two 5" tracks like Carl suggested and pulled the pins on the 3 Red tracks that extend just past the edge of the lift-out, you wouldn't have to cut anything, bench work or track. Add a similar cleat to the other side and the lift-out would simply rest on the cleats. I don't see any reason whole tracks need to be on the lift-out, especially with FasTrack. If I'm wrong, I'm sure Carl and Jan will let me know. 
