Thanks guys,
I figured as much as hard coding the parent path 
But, Eric’s last suggestion is perfect, it works great.
It looks like Ruby is quite powerful as long as you know it, like C++. For those of us who don’t, and don’t want to waste Eric’s time - how about sticking a few more examples like this in the OOD User’s Guide?
Or, link to implementations on other sites. E.g. I am working on a document to share with our Rocky Mountain group where I am putting the local trickery, https://github.com/CHPC-UofU/OnDemand-info.
Thanks,
MC