in my office our structural department usually placed these supports .  I have tried to get the support to read the pipe elevation in the past and have not been successful. you're trying to read parameters from 2 different categories, which Revit typically has issues doing without additional programing. 

• you can try to trick revit by modeling the Pipe Support as a "Pipe Fitting" or "Pipe Accessory" and see if you can get it to read the elevation from the pipe.
  • i started to try that a while back but got busy and didn't finish .
• you can use a program like Dynamo to write a script to Read the pipe bottom elevation and apply it to the support height (probably have better success with this option ).