Very interesting...
This is being explored here too - do you fancy joining in that conversation too?
It would be interesting to try that using rclone's app id and see if it works.
x-amzn-clouddrive-source: XXXXX
x-amz-access-token: XXXXX
x-amz-clouddrive-appid: XXX
x-amzn-RequestId: XXXX
So that might be part of a new API...
I applied to join the new API program but was rejected - your app might need to be part of that I guess...