Openings in Existing PT Slabs

I am trying to add an opening to an existing PT slab. I have modeled the existing tendons and appropriate profiles. I want to add an opening so that it does not change the exisitng tendon profiles, but if I model the tendons using the tendon parameters and add a tendon void/opening, it automatically places the tendons at slab mid height. If I model the tendons manually, I do not know what the exact tendon elevation is at the opening edges and cannot break the tendons at the opening edge along a given profile. Any suggestions?