I made a Pull Request to repo2docker which I think will fix this: https://github.com/jupyter/repo2docker/pull/646 if any of you have a moment to test drive this locally that would be great.
I think you’d need to run repo2docker --uid 1000 --user jovyan https://github.com/binder-examples/r to do so. It will take quite a while as it has to compile all of the tidyverse :-/