In our latest implementation, customer has requested to disable the Attachment in CRM as they want all users to upload the documents to SharePoint (via the Document Management integration).

However, CRM does not have configuration to disable attachment.

Hiding the Attachment icon is unsupported and risky.
Thus we wrote a plug-in to prevent users from uploading files via CRM.

However, the error thrown during attachment upload is not a friendly error (unlike the standard entity edit forms).
Please see attached screenshot for details.

Can MS enhance the /Attachment/upload.aspx page to show friendly error from exception thrown via Plugin?
Or is there an alternative workaround that is supported?