Have a look at example 2 from this page: http://support.sas.com/kb/40/781.html .
It sets the parameter objects to certain values before running code, and you should be able to use it as a starting point.
This page http://support.sas.com/documentation/onlinedoc/guide/ has a download (albeit for EG 4.1) that outlines the object model EG uses, but should let you see the other variables available for each object (e.g. the Parameter name or default value, etc.).
I've never really had to do this level of automation beyond some minor tinkering, so I don't have anything pre-written that you could base this on, but hopefully the above should give you a start (unless of course someone else has some pre-written code for you!).
