Polycom- Two calls from same registration on different keys

I’ve been trying this for a very long time with no success. This applies to all Polycom IP phones.

I’ve configured one call per line key by editing reg.x.callsperlinekey. Now I would like that when another call comes in from the same registration, it should ring on the next line key.

Obviously, I also edited reg.x.linekeys to the max in order to let other line keys on the phone be associated with the same registration.

I cannot believe that this is not supported, as most most phone systems will let you toggle/handle different calls via different keys.

The best I could do for now, is just use call waiting via the same line key.

I would greatly appreciate any input on this matter!!