You can generate that GPX in two different ways, both of which would require you to be a paying member of Project-GC:
1. Using Map Compare.
First set up a custom filter using the link under your username. Set the Cache Owner setting into a statement for that filter.
Create a separate VGPS for this list to go into.
Go into Map Compare. Set yourself and the other cacher as the two to compare. Set the area. Select "None found" only for the "Show" options. Add custom filter and select the one you created. After you've filtered, select all and add to VGPS.
2. Using just the VGPS.
Create a new list (assuming you didn't do this for the initial list). Provide the list of GC codes to create this list. Sort by Owner. Do a multi-select of the caches not owned by the specific owner you want (using Shift+click to select a block) and delete them.