How to calibrate the non-zero THRU in TRL calibration?

In TRL calibration, THRU standards is applied to set the measurement reference plane, if the THRU is non-zero length, the reference plane is set to the middle of it. However, I want to calibrate the reference plane to the probe tips, while i only have non-zero THRU standard and other reflect and line standards. So, how can i offset the non-zero-length-THRU-induced effect on the calibration? A Cascade engineer told me to simply configure the delay time of the THRU standard in their calkit. But i don't know whether this may cause any errors, cause the delay time can be utilized to offset the insertion phase, but the magnitude of the insertion loss caused by the non-zero-thru standard is still not known,i guess. So am i wrong, and what should i do to set the reference plane to the probe tips? any reply will be appreciated!

could anybody possibly help me out,plz...

Maybe this homepage helps: http://na.tm.agilent.com/pna/help/latest/S3_Cals/TRL_Calibration.htm