Radu,
This is supported in Stardog 7.1.2. You can now import JSON and CSV files using SMS2 mappings with the HTTP API. Here is how it might be used from the command line with cURL:
curl -u admin:admin -F "database=foo" \
-F "mappings=<mappings.sms" \
-F "input_file_type=JSON" \
-F named_graph=urn:ng \
-F "input_file=<data_file.json" \
http://localhost:5820/admin/virtual_graphs/import