With some copy and paste of code from this page, I quickly had a MediaWiki Special Page set up, where I could make use SMWWriters internal API to implement a crude form for adding or removing "triples" in my Semantic MediaWiki. See Screenshot:
And the result, on the Methane page:
Looks promising. Connecting this with some ARC functionality for parsing SPARQL and RDF/XML, should make a big step in the right direction.