This turned out to be pretty straightforward to implement and is now done! Check out the new plugin version 2.12.13 which includes geographic search filters on shortcodes and blocks. You can stipulate a pickup postal/zip code and radius, which when set will only display items available for pickup within this radius.
Note, when the pickup filters are set only eBay items marked as available for pickup will be returned. It will also override the Search Location filter that returns items deliverable to given regions.
I hope that serves your needs, let us know if you encounter any issues or have further feedback. If you find this new functionality useful, do consider leaving a review for my plugin, it would be much appreciated.
Arthur.