Are you wanting to do this instead of migrating a particular workflow to every list?

It's for a custom list/tool I have to create every so often that also needs to have a workflow attached to it. I can automate the list creation easily enough but automating the workflow creation is drawing some blanks.

you should be able to do that if you called directly Workflow.asmx webservice.

see reference and several PublishWorkflow functions here http://help.nintex.com/en-US/sdks/sdk2013/#Reference/SOAP/NW_REF_SOAP_NAV.htm%3FTocPath%3DNintex%2520Software%2520Develo…