What are my next steps when trying to join a server to a DMZ domain and can only see RODCs?

Hello,

We are trying to join a server to a domain.  The domain is a DMZ domain with 2 R/W and 2 RODCs.  The server we are trying to join only has the AD ports open to the RODC and is 'firewalled off' from the R/Ws. 

I've prestaged the Computer Account on the R/W and pre-populated its password on the RODC, so the Computer Account is part of the Password Replication Policy and shows up in the 'Accounts whose passwords are stored on this Read-only Domain Controller.

What are my next steps here to join the Computer object to the domain given I can only see RODCs and am 'Firewalled off' from the R/W DCs?

Thanks for your help! SdeDot