There appears to be a little more flexibility in the SRA's approach. Hitherto we had understood that the supervisor had to be someone who directly supervised the applicant's work. Indeed we had been told that if the applicant had no such person the application for exemption would not be granted and they would have to sit & pass the SQE2 exam.
However, we recently have received a reply from the SRA which indicates that they MAY apply a slightly more lenient approach. They might 'consider a supporting reference from an appropriate third party'
Below is an image of their reply.

SQE2 Exemption Applications - Qualified Lawyers
https://hunningsconsultancy.co.uk/sqe2-exemption-for-foreign-lawyers-review-advice/
External QWE Confirmation Service
If you know of someone who needs an SRA regulated solicitor to confirm their QWE but have no-one in their organisation to do so - we can help. This service would apply to someone who is NOT qualified as a lawyer. Please see the link below and feel free to signpost them to us: QWE - External Confirming Solicitor Service - for Aspiring Solicitors
YouTube Videos on SQE, SQE2 Exemptions & QWE