I actually figured this out myself. To show ALL customers including the contacts which are linked to a company or other person, go to Debug->SearchView and change from this line

<filter string="Customers" name="customer" domain="[('customer','=',1), ('parent_id', '=', False)]"/>

to

<filter string="Customers" name="customer" domain="[('customer','=',1)]"/>

(just remove the ", ('parent_id', '=', False)" part)

This small change allows you to search for any name found in the customer list including the contacts.

Make sure the Is a Customer checkbox on the Sales & Purchases Tab of the Contact is checked:

You will have to open the Contact directly, not open it from within the Company it is attached to.  To do this clear the Customers filter and search for it by name.