You are correct that it can't be.
The feature/option has been requested but hasn't happened yet.
I also think Shaw has 'moved-on' from the Gateway product and we won't see much more for updates on it..
They promised for years after the Gateway and DCX3510 PVRs came out that the Expander bug in the DCX3400s would be fixed, but that never happened either.
My honest opinion is don't expect any more feature updates to the Gateway system.