Possible to set OrderDetail1 to a Foreign Key?

 Hello, I use some custom stuff in the Portal to write the approver into the orderdetail1 field for a request and then use an approval workflow that picks up on the orderdetail1 field so that the approver is the one selected in the portal. That works fine. My problem is that I need to send a notification that includes details about the approver (phone number, name, etc). The problem is that in the Mail Template, when I try to use OrderDetail1 as a Foreign Key using the $ notation I get an error saying that "OrderDetail1 is not a foreign key column". Is there a way to set it so that it is a foreign key column? Maybe in the DialogColumn table or something but I don't want to mess around with it without knowing exactly what to do. Or else, is there a way to get the information about the person whose UID is in OrderDetail1 into the mail template without using the $ notation?