It is quite amazing that the CAA endorse a privilege on a licence and like a cheap Chineese product on eBay, it comes with nio instructions!
No, you cannot ever sign your own licence, other than as the licence holder.
As a FI, I am surre there are enough alternate options that you can use, as opposed to flying with another FI, to revalidate your SEP class rating, and simply get it signed by an Examiner.