How to support flexible tube.

Hi-

I am doing a 3D FSI model on a simple branched artery with blood flow. I naturally want the artery to expand and contract as the fluid moves though. What is the best way to constrain the inlets / outlets? Rollers do not add enough constraint and fixed edges constrict the artery from expanding / contracting. In addition, I get high stresses at the areas of constraint.

Attached is a picture of the geometry where the arrows are the fluid flow

Thanks,
Barrett