Has anyone come up with a way to make an MRE session timeout after 'n' minutes of inactivity?

If you are using the BI Dashboard interface to MRE, you can setup the appropriate servlet parameters.
In 5.2 release the servlet is named WORP_Loader (in 4.3.6 it was WORP_RM), the parameters are USER_MAX_INACTIVE and PUBLIC_MAX_INACTIVE. They have a clear description of their meaning in the web.xml file. They are also described within the "WebFOCUS Managed Reporting Administration Manual" (release 5.2.3, chapter 5).
The parameters has no influence on session expiration when MRE is accessed through the java applet interface (/ibi_html/workbnch/mrlogon.htm).

Hope this helps
Grzegorz