Roadway Designer Target Aliasing

Perhaps I am trying to use the wrong tool to do this, but I am having an issue trying to get my side slopes to draw correctly. I have a diamond interchange and I am currently modeling the ramps. I have a corridor "complete" for the mailine and the existing ground surface. When I am doing my ramps, I want the side slopes on one side to target the mainline corridor and on the other side target the existing ground surface. What is the best was to do this?

Thanks for any help provided,

Ken