How to prevent incorrect PA coding in the invoice and requisition screens?

We have our profile 'PA: Allow Override of PA Distributions in AP/PO' set to "No" sitewide. As expected, this prevents users from updating the account field once they have entered a project/task/expenditure type and the account field is defaulted in based upon information in the Projects module.

However, nothing is preventing a user from directly entering a PA project directly into the account field along with other incorrect account information. For example:

Project number 65. In the Projects module, the default coding for this project is: 001-123456-0000-65.

If a user enters 002-654321-0001-65 directly into the account field of the invoice (incorrectly), the system allows this and by dynamic insertion this string is now considered valid in our account combinations.