The subsidiary field is multiple-select but does not allow the search of subsidiaries and is very difficult to use, especially in the context of a large organization with large amounts of subsidiaries and accounts.

The solution I have put together works in 3 steps:

1) A Suitelet that creates a Matrix of all subsidiaries and accounts.  Down the 1st column are the Accounts and across the 1st row are the Subsidiaries.  The Matrix entries are simply X's.  The Matrix is a CSV file and when created is stored in the file cabinet and sent to the user by email.

2) A set of Excel VBA macros that creates the necessary CSV file for updating the Subsidiaries per Account via CSV upload, following the user update of the Matrix in Excel.

3) A CSV update import mapping.