I presume you have all of that expression in an excel file, right? Is so, What are its columns and how do you represent the fields and calculations on it?
About your question on "where it should be", maybe you can create your own project that references only the ORMSupportClasses.
When you load your excel, somehow you have to translate those calculations into some expression system. Like "Customer.CustomerId" translates into a EntityFieldCore, the "+" sign translates into a Sum operator, etc.
Then, 'somehow' you should traverse store that in a Dictionary<EntityFieldCore, Expression>, where expression is some class that store the operations graph, etc. I think you have all that figured out. Where to place it? As I said before, I would put it in a separate "Calculations" project. You can't put it on the Generic generated project because you don't now the operations in advance.