Attach Rail Options w/ Sweep2 command

This may be basic, but what is the workflow for creating a sweep by using an existing curve from a Brep and attaching curvature through the 'rail curve options'. This is how it is made in Rhino of course, but can't figure this out parametrically.

I have created a BRep surface, I have exploded the components and culled the edge of the surface I want to use and swept using that as a rail...But I can't seem to find the right option or method to give me surface curvature matching.

Thanks in advance.
Paxton