Invoice validation check

We create a customized role from Accounts Payables Specialist and delete from the copied role the options for Validation
The Role works fine from the Create Invoice UI. User can create invoice and option for Validate was not available. But, the problem is when enter to Invoices UI and select an invoice, the Validate button is available.
We need to hide or eliminate the Validate button since this Customized Role should not validate invoices.
Question is how can I delete/hide a button from Invoice UI for a specific role?