Maintaining vertical orientation of extruded meshes

[rickgplus]

Is it possible to maintain vertical geometry when extruding a mesh along a spline?

I am trying to build a wall with vertical posts/ slats. But they will bend along curves that travel up or down. Looks as expected if the CPs are all on the same plane, but i need to travel up and down hills.

I've tried different orientation methods and rotating CPs, but have not found the right combination to keep things completely vertical.