You want the guide to be able to rotate.
Machine the end plug to look something like this:
http://www.airgunspares.com/store/pr...-Part-No.-V15/

Then you can make a rear guide with an end flange, and a hole that fits over the stub you left on the end plug.
Add a thin steel washer between the delring guide and the end plug to facilitate rotation.
Make the guide about 0.05mm larger than the spring ID for a really tight push fit. This may reduce power a bit, but will kill most vibration without adding lagre amounts of grease.