Use the Create XML module before this and you will add the required parameters (you want to also strip the xml declaration from the advanced settings if you use this module).
You can put directly in the XML body (I haven't tested this one specifically but should get you close) or can do a set variable and create as XML format:
<StageIDs>
<item>4417751</item>
</StageIDs>
<WorkflowTemplateID>4556</WorkflowTemplateID>