Restrict internal bank account access within an OU

I know this has been asked several times before with no answer but in the hope that someone has worked out how to do it:

Does anyone know how to restrict access to internal bank accounts within an OU?

Example:

I have two bank accounts both owned by Legal Entity A. Operating Unit X has access to both accounts, but Bank Account 1 is used only by Payables and Bank Account 2 is used only by Receivables.

What I need is to be able to create two Cash Management responsibilities, one which can see only Bank Account 1 and one which can see only Bank Account 2.