You may be interested to know that EASA NPA 2014-29(A) proposes to add a Section to Subpart K to Part-FCL as follows:
SECTION 8 SPECIFIC REQUIREMENTS FOR THE SENIOR EXAMINER — SE
FCL.1035.SE SE privileges and conditions
(a) Senior examiners specifically authorised by the competent authority to observe skill tests or proficiency checks for the revalidation of examiner certificates shall:
(1) prove an examiner experience level in accordance with the procedures established by the competent authority;
(2) have conducted a number of skill tests or proficiency checks as a Part-FCL examiner;
(3) have successfully completed a senior examiner course at the competent authority; and
(4) demonstrate their competence to the competent authority through an assessment of competence.
(b) The validity of the authorisation shall not exceed the validity of the examiner’s certificate, and in any case shall not exceed 3 years. The authorisation may be revalidated in accordance with the procedures established by the competent authority.
This appears to be broadly similar to the relevant AMC that I quoted earlier in the thread.