Are you still needing this?
I have a little app which is doing this as a sample using c#.
It's not by any means production grade code but it succinctly demonstrates how to do the following in c#
1) connect to VSOWebControlService
2) generate WorkflowTokenAttributes
3) load plugins
4) execute a workflow
5) wait for a workflow
6) respond to a workflow
I haven't worked out how to make async calls yet but likely I will have this sorted in a day or so.
pm me if your still in need of this.