Nick,
Have you read the presentation by Bruce Powel Douglass "Computational SysML Models"? He addresses the use of Constraint Blocks and Parametric Diagrams in support of trade studies. The relevant material begins on slide 12. Here is a link to that presentation: 7b138411-6bc0-462a-b459-c6c440d1a3d6.filesusr.com/.../21dc4f_4634297c8c644b7886a9ced5b0e56fb0.pdf
Bruce's book "Agile Systems Engineering" contains considerably more insights on his approach to performing model-based trade studies on the system's architecture candidates.
Apologies if I have misunderstood your need.