Custom Invoice Fields - Multiple Contacts

I have the below line showing contact one first name and last name,

"text": "$contact.firstName $contact.lastName"

ideally i am looking for something like :

"text": "$ $ $contact.two.firstName $contact.two.lastName"

So that I can show both contact’s as the addressee on an invoice, is this possible at all with any custom code the custom invoice designer or somewhere in the back-end where i can modify the PHP?

I don’t think it will be possible, or at least not without large changes to the code.