Account Reconciliation Balance load

I receive a file from a vendor that contains transaction details, transaction amounts, and a running balance. I can load the transaction records into Transaction Matching without any issues.

In addition to the transactions, I also need to load the final running balance from the file as the sub-system balance. Since the running balance is cumulative, I only need the value from the last record in the file.

Is there a way to configure the import so that only the last line of the file is loaded as the sub-system balance?

I tried using a CASE statement with a MAX