In External Diff tool, can I get the path to the file?

[TamarGranor]

Four years ago, I built a little EXE to use for external diffs that let me apply BeyondCompare to the paired files that represent various things in Visual FoxPro. Along the way, I ran into the fact that the $REMOTE parameter passed into external diffs is relative to the repository's home folder. (I asked about that then: https://community.atlassian.com/t5/Sourcetree-questions/Custom-diff-tool-finding-the-REMOTE-file/qaq-p/1551704)

Back then, I found a workaround in VFP that let the thing work for me. Now, I have a new computer and that workaround isn't working anymore.

Is there a way to get my hands on the repository's home folder? If I had that, I'm pretty sure I can do the rest.

Alternatively, is there any way to specify that $REMOTE include a full path?

Thanks, Tamar