Easy method for obtaining luminis domain within the XSL of a channel
Well making some changes to the email channel (found in $CP_WEBINF/cars/email.car) to have the links take you into Horde/IMP I came across the following XSL extension that sungard has created.
cpExtension:formURL(aString)
What this does is create a URL on the Luminis server. You pass it the path to the file/script/image/etc and it will but in the appropriate http://servername/ piece at the start. The path you include needs to start from the root of the server, so no relative pathing.
It seems there are a number of options under the cpExtension umbrella too bad they are not documented.

Good find. Any idea if this
Good find. Any idea if this can be used in nested-tables.xsl? Also, could you post a sample of how you're using it?
Re: Nested-tables possibly
In the XSL that I found this in (emailchannel.xsl from email.car) they had the following in the xsl:stylesheet element indicating the various additional name spaces:
xmlns:cp="http://www.campuspipeline.com"
xmlns:cpExtension="com.pipeline.web.WebUtil"
xmlns:cpInfoExtension="campuspipeline.uportal.dlm.provider.ExtensionClass"
extension-element-prefixes="cpExtension cpInfoExtension"
exclude-result-prefixes="cpExtension cpInfoExtension"
So in theory you could try adding that to the xsl:stylesheet element in nested-tables.
Then to use it I am doing this (once again from the emailchannel.csl)
<xsl:value-of select="cpExtension:formURL(string('/cp/ip/login'))"/>
which will output http://luminis/cp/ip/login if I am currently on the domain luminis.