Enable the API to update an 'Auto Receptionist' to route to an external contact

We have successfully used the API to create on mass approximately 2,000 ‘External Contacts’ and ‘Auto Receptionists’. As part of this automation we need to route the Auto Receptionist (AR) to its corresponding External Contact which in turn is set to route down our BYOP SIP trunk to our on-premise PBX.

It seems that there is no obvious supported way to do this via the API. We have reverse engineered an AR that configured via the web portal and worked out that the routing option is done in the Call Handling API. However, when trying to use the PATCH/POST to add/update a call handling setting it seems that routing is not available.

Is there any way that this could be acheived via the API or is it a new feature?

Many thanks,