Property Tab Builder drop down list: Relative Filepaths?

When linking to an excel or txt file to populate a drop down menu in a custom property, so far I've only been able to use absolute paths, as so:

Absolute paths create problems when the files are moved, reorganised, or accessed over the network by varying computers, so relative paths would be really nice here.

Greatly appreciate any help on this item! Thanks.

SolidworksDrawings And Detailing