single workflow for same list in different subsites (SP 2013 Workflow)

Question

I have the following structure in my Sharepoint:

• Parent Site (site collection)
  • Project A (subsite)
    • Orders List
  • Project B (subsite)
    • Orders List
  • Project C (subsite)
    • Orders List

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Orders List is the same for all subsites. I'd like to create a single workflow that will work for all Orders List. If I create a workflow for each list on each subsite, maintenance will be hard.. Will have to update all workflows separately once one is changed.

I've looked into workflow attached to content types but it doesn't work in SP 2013 Workflow.

What is the best way I can do this? Maybe create a workflow on the parent site that works for all subsites calling same list.