I 'm using following step.
1) Duplicate a stereo record to another document.
2) Split the stereo record to 2 monaural record.
3) Invert phase of R.
4) Merge with previous track to be a stereo document again.
5) Convert (mix) the stereo track to a monaural record. (L-R)
6) Add new stereo track to the document.
7) Copy the original stereo record to the new stereo track.
Convert (mix) the stereo track to a monaural record. (L+R)9) Merge with previous track to make stereo document.
Is there any simpler way ?