Start a workflow from the ECB

Question

I want to add a custom action to the ECB to start a workflow automatically. To get to the workflow page I can do something like:

<UrlAction Url="/_layouts/Workflow.aspx?ID={ItemId}&amp;List={ListId}"/>

I can’t work out how to start a workflow automatically rather than go to the workflow page.

What is the syntax that I would need?