Extrude EDGES....but in stair step increments rather than linear. Works best with borders / external edges. Can work with internal edges but not advisable.
Remember, for perfectly straight lines, you need to 'nudge' it a little bit...why ? Dunno, not a programmer/coder....I just do whatever it takes to get around a problem.
http://www.vusta.com.au/
(link on Houdini page)
Note in the second pic, the effect can be achieved with 2 nodes...one goes up then one goes down.