GPX upload x3g with stock Makerbot firmware (non-Sailfish)?

Hi all,

I know the release notes for GPX say

Upload to SD doesn't work. It can't work directly because SailFish removed that feature to save bytes. Probably a good call since who wants to wait for 115200 baud when you can just plug the SD card into your PC.

But what if you're running the stock Makerbot firmware? I try uploading and the Files pane looks like it's uploading, but it never works.