Send secondary order confirm to customer defined email address?

When my customers complete their order I wish to have a copy of the order sent to their boss for approval. Technically I understand that I can simply add a second recipient in the conditional action triggered by them checking out (E-mail customer checkout notification). But, since it needs to be dynamic, I need to get their email address into one of the available token replacement patterns.

The only fields I am capturing at checkout are:
First Name
Last name
Department
Building
Room Number
Supervisor Email

I am thinking I could simply change the Shipping Address field [order-shipping-address] to Supervisor Email but it would be cleaner if I could simply add a Secondary Email field. How would I best do this? Thanks.