Set up a table to hold the file paths - it needs three columns:
ID - primary key. Into is probably fine, as is Identity
CustomerId - type matches that in customer table and is a foreign key
Path - nvarchar
I would probably add an OriginalFileName and a VersionNumber field, and store the file under a Guid name rather than the original name (so it's easier for different customers to have different files with the same name.
You then retrieve the files by searching for the customer is.