How to set the outgoing phone number for a bot when calling a PSTN number via direct routing

One of our applications initiates outgoing PSTN calls using POST https://graph.microsoft.com/v1.0/communications/calls as bot resource. The bot resource has a direct routing phone number assigned. How can we define another outgoing phone number? In our use case we would like to initiate the outgoing calls using an employees personal phone number. The bot is used to set up the call on behalf of the user. Therefore we would like to ensure the callee sees the callers phone number instead of the number of the bot. The personal phone numbers are already configured & working in teams. As we can select the outgoing number in teams, we hope to be able to select the outgoing number for calls initiated via bot too.