Can I use Process Builder to copy a master detail field from the parent to the child?

Hi,

I am trying to use Process Builder to Create a Opportunity (Custom Opportunity object) when the parent Customer record has a certain field set as true.

The problem I am having is that, the Master Detail field on the child Opportunity record that uses the name of the parent Customer Object needs to be populated as it is a required field having been created as a master detail field.

The options I see when creating this new Opportunity record, for the field Customer name are to use ID, Reference or Formula (I am assuming this is the route I need to go down).

Any ideas or help on how I cna get this Child record to be populated with the Parent Customer Name?

Thanks