GTM Sync Group for Standalone GTMs

Hi, we have 4 standalone GTMs in our network that are installed in 2 different data centers. Each non-HA GTM pair are behind a pair of HA LTMs. So the GTMs are in Active/Active state and I have a question about the sync group.

 

 

When configuring the sync group, I can create a sync name but I'm not able to hard code the IP's of the other standalone GTMs so how can I configure the sync group in this scenario so that the GTMs are synchronizing their configuration so I only make Wide IP updates on one box?

 

 

Thanks if you can help!!