Getting Form Field Values as a dropdown in custom workflow field

Hi all,
Various docs and some custom solutions from people with custom Workflows are outdated a lot with being Version 7 etc.

I can create a custom field in the workflow and put the system name of the field as a text string and read it all good.
I can create dropdowns that have member groups populated in them etc.

I do not seem to be able to work out how to get all the form fields like on the default workflows for mapping as a dropdown that will return the system field name.

Can anyone help?

Close to finishing a useable updated member workflow that if solid I can share as an package.


This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/106445-getting-form-field-values-as-a-dropdown-in-custom-workflow-field