Currenlty theres no api-available for doing such things. Currenlty there exist some REST-Services to signalling a task to the end and to reassign a task as well. More comfortable would be to have an appropriated api.
The easist way to implement a uncoupled-interaction with remote-services would be to implement the appropriated Webscripts. This is likely more easier than building up /extending SOAP-Webservices for this manner.