Using SubversionSCM excludedRegions of SVN externals

I am unable to get the SubversionSCM excludedRegions to work with externals in my Subversion repository when using Poll SCM. I can successfully use excludedRegions if the directory is part of the main repository but not an external repository which has a different root repository URL.

One less than ideal option is to just do Subversion checkouts of the individual directories from the main repository and external repositories. This is potentially error prone, in addition to time consuming if directories are changed or added.

The cleanest option I came up with was to use a script to poll the SVN repositories while using the Trigger builds remotely option.

I have solutions but would like to use excludedRegions as this seems like it would be the most straightforward solution. Does anyone have any suggestions?