Cisco DPC3941B and port forwarding

Hello,

It looks like I posted originally in the wrong subforum so perhaps posting in here can help me out.

We have a DPC3941B and tryign to setup port forwarding where an external port routes to a different internal port - for example port 5555 would route to port 80 internally on a specific server.

It appears the DPC3941B does not allow that - we can only setup a port range that is the same externally as it is internally. 

Aside from going bridge-mode and buying my own router - can the DPC3941B be modified to do proper port forwarding?

Thanks!