EPM & Aastra adding an additional line/extension to a phone

Running 5.211.65-20 distro with commercial endpoint manager and Aastra 6865 endpoints.

Is there a way to add an additional line/extension to each of the telephones from within the endpoint manager?

Would like to be able to receive a second call if I already have a call in progress. User is waiting for a consult with another internal user. For example, a user will have extension 201 appearing on the 2 line buttons, then add a 3rd line with extension 4201 for an internal consult.

I can see in the endpoint manager where I can select a line as an option, but I cant see how to map the extension to that button

Can this be done within the EPM, if so, can it be done with one template for all or do I have to create a template for each user?

Call waiting is causing the speakerphone to engage when on an existing call if a second call rings - user has to be aware and hit the hookswitch to go back to handset. Looking for a workaround for this issue.