I have made a small chunk of code (@ https://github.com/addshore/wmf-grafana-json-datasource) which should present a simple API which can be used by the grafana simple JSON datasource plugin.

The small amount of code allows Dashiki style annotations to be included on grafana graphs.
Sample dashiki annotations can be found at https://meta.wikimedia.org/wiki/Dashiki:PageviewsAnnotations

The simple JSON data source should be added to the labs grafana instance https://github.com/grafana/simple-json-datasource
And a datasource should be added pointing to the URL http://tools.wmflabs.org/grafana-json-datasource/