Is there any way to define Open Ports without limiting it to a particular WAN interface?

I now have WAN1 and WAN2 working on different lines and I need that most of my open port settings should work identically on both interfaces.

It seems that I can only set one index entry to one interface or the other but not both.

As I have already used up 14 of the 20 entries, I can't replicate all the WAN1 entries for WAN2 (as well as the duplication is not a good idea for maintenance).

Is there some way to do this? Maybe by Telnet?