How to retrieve Portal User status from DESK into CRM?

How to retrieve Portal User status from DESK into CRM?

Hello,
We are using CRM and DESK in 2-way sync configuration, meaning Contacts in CRM and in DESK are in sync.
When we invite a contact in DESK to be an "End-User", he/she can then access the Help Center. 
Such invited contacts can then be found in lists and reports by using a system field called "IsPortalUser" , which is now IsEndUser in the new API if I am not wrong.
Unfortunately, this system field IsPortal can not be selected in the sync settings between DESK and CRM so there is no easy way to bring back this IsPortalUser information into CRM.
I am looking for ideas/suggestions on how to do that.
Thanks!