My suggested steps:
1. Finish installation of open server with real IP (later used for bond) assigned to any of available interface
2. Once installation is done, connect over console
3. On console, remove the desired IP from current interface (you will be able to connect ONLY using console connection)
4. Create bond interface and assign to bond the desired IP
5. Check/correct default route
6. shutdown the former interface used (if not part of bond)
7. Finish First Time Wizard
Kind regards,
Jozko Mrkvicka