It is unclear how, exactly, to set up Workbench so that you can access a remote SPARQL endpoint. The "Remote RDF Store" option uses HTTPRepository, and I haven't been able to figure out how to point it to a non-Sesame SPARQL endpoint using Workbench.
Perhaps the issue is that the Workbench (and Console) are focused on referring to Sesame instances with a URL structure that is a superset of that of the SPARQL endpoint standard. Possible fix:
Add a SPARQL endpoint configuration option, sparql.ttl, for SPARQLRepository, very similar to the remote.ttl for HTTPRepository.