Dear Peter,
during bank statement creation this is not possible to enter a cost center (this UI supports you in entering the bank statement) .
What you can do instead:
1. Repost the bank charges with a manual JEV.
2. Do the assignment in the payment allocation (do not provide the bank charges in the UI field). Remark: you need to do this with the "other alloactions"
Maybe it is worth an idea in the SAP ideasplace?
Best regards
Marlene