Andrew Turpin

So turns out this is totally doable...

1. Set up your Zendesk app in Okta with provisioning enabled using Zendesk JSON Web token SSO
2.  Create the needed User Field in Zendesk (people -> User Field)  
3. In Okta go to the Zendesk app on the provisioning tab, click on the "Go to Profile Editor"
4. In Profile Editor click +Add Attribute, refresh  Attributes list, and then select the new User fields
5. In the Profile Editor click Mappings and set the needed attributes in "Okta User to Zendesk"
6. Profit

Adding my voice to the mix as this would be very useful for us as well. In our case we have one ZD for external support and one for internal support and keeping them separate is essential.