We made a release this afternoon and now every file written to the volume will belong to/owned by the group id 1000.
(this one is the default when you create a new user outside of root on debian/ubuntu).
So you can go ahead and re-deploy your app without root, if you create a user in the container like so useradd -u 1000 -U app it will own the files in the volume.
Let me know if I am not clear enough, and you need more explanation.