http://www.nppl.uk.com/documents/AOPA-UKNPPLAmdt08.pdf is the Second Edition of the NPPL SSEA syllabus to which you refer.
Your colleague's proposed course of action sounds fine - I would recommend that he also sends in a copy of the 'Additional Rating' form but makes it clear that he has been using JAR-FCL SEP Class Rating privileges to fly Microlights as per LASORS C1.1.
Let me know when the application is submitted to NPLG and I will contact them to confirm what has been said.
Your colleague will need to include logbook evidence of his SEP and Microlight flying, plus a photocopy of the relevant pages from his JAR-FCL PPL.