Populating Test Data Container in eCATT without developer access

I'm new to eCATT and I'm trying to figure out how testers without developer access can supply structured test data for the test execution.

It looks like to maintain values in test data container you need developer authorization. Creating test data variant as external file won't work if you need to pass deep structure.

Even to change variant values via API methods you need S_DEVELOP authorization.

What am I missing here? How can testers upload their own test data without populating it manually in test configuration?