Michael,
If you go to the All Gauge Toy Train Association web page, (www.AGTTA.com) and look in the Tech Tip tab for Teck tip #2, or the Newletter link for the April 2010 newsletter, there is a Tech Tip article on how to mount and add the relay. In the article a metal bracket is used to attach the relay to the other side of the E-Unit mount. Take a look, it might be the info you need.
Ross