Using Purl on prefixed paths?

Hi.

I have a site (http://crca.org.au) on which we currently have details of congregations (organic group nodes) under AboutUs/WhoWeAre/Locations/. I'm wanting to use Spaces and Features and so on to give each congregation optional support for blogs, uploads and so on. When I try to enable this, however, my congregation links end up becoming white screens of death, with urls like:

http://crca/boxhill/AboutUs/WhoWeAre/Locations/BoxHill

I'm assuming this is because I somehow need to get PURL to treat "AboutUs/WhoWeAre/Locations/" as a static prefix to the persistent bit. Is this possible?

Regards,

Nigel