If you don`t want to deform geometry, you must take another approach.
You could use an extra subspline for railing with a different ID (set limit by ID on Generators).
Detach the handrail from the posts and use it as a separate segment. I have used RC Slice to get the Default Segment.
Finally, since the connection between start/end and default segments is not perfect you could use Vertex veld to veld it together. (Before adding any modifier on top of the RC switch dispaly mode to Mesh)