It just doesn't work, since it's a special drf<->tastypie compatibility layer. I hoped it would initially, but it doesn't, and since it might trip up people expecting it to work in the future I figured I'd raise `NotImplementedError`

For the record, we could probably implement it instead of my `extra_fields` hack, but it would be so annoying that I think it'd be better to just switch completely to DRF :)