Multiselect allow duplicates

Hey there, I have a select setup as a relationship and multiselect, but I want to allow the same relation to be made more than once. As an example of the use case, An order can have many products but also have more than one of the same product. Is there any way to allow this?
Also, as a tangential, is there any way of adding pivot values to the entries in the multi select?
Thanks!