From what I understand - the Datacentre folks are asking you to place both 0/0 and 0/4 in the same L2 segment. This can be done usign Bgroup interfaces. You must have some predefined ones on your Firewall already.
What you need to do:
- Remove IP from e0/0
- add 0/0 and 0/4 to any bgroup interface (bg0)
- assign the 192.168.100.x/24 IP, zone etc., to the bg0 interface. In simple terms, migrate whatever configuration you had on e0/0 to bg0 - IP, routes etc.,