Our toolshed tools include a custom display application.  Although the display application is open source ( https://bitbucket.org/Andrew_Brock/proteomics-visualise ) we do not yet have a public server for it.  Actually, at present it isn't possible to have the application work properly if it is running on a completely separate server because it needs access to galaxy's database/files directory (I'll leave that for another question).  For now I just need to be able to provide a way for administrators of a local galaxy to configure the url to this display application. 

At the moment we have it hard coded .. like this;

 <url target_frame="galaxy_main">http://${galaxy_url.qp}:8500/init_local?file=${encoded_filename.qp}&amp;type=mzml</url>

Using the galaxy_url (because we are on the same server) .. and hard coding the port.

What would be the best way to allow local admins to configure this? 

Thanks

Ira