I'm pretty sure it's not possible with the plugin as it is now—in fact, it may not be possible with Taverna as it is now (since there's no support for RDF as a datatype and no way to read in an RDF file, at least last time I looked…)
"<uri-of-subject>
data in N3..."
So, for example:
"<http://lsrn.org/UniProt:P12345>
@prefix lsrn: <http://purl.oclc.org/SADI/LSRN/> .
@prefix sio: <http://semanticscience.org/resource/> .
<http://lsrn.org/UniProt:P12345>
a lsrn:UniProt_Record ;
sio:SIO_000671
[ a lsrn:UniProt_Identifier ;
sio:SIO_000300 "P12345"
] ."
Or you can send a list of those strings.
You could use a constant or a beanshell to produce the appropriate string.