Off course, I'm not talking about making them hard-coded, but optional.
We all know that there is providers out there, that do not honour the SIP standar and did "their things". but the Diversion Headers on FusionPBX should be simple to let them work as optional from the gateway menu, for example.
It doesn't work, when a call to an extension, part of a ring group or ivr, have set the call forward to external number, it do the forward, but doesn't set the diversion header.
Only on direct calls to the extension, the diversion header is set.