No the student in question cannot get a validation since he already holds a US certificate, his CPL SE.
You cannot hold a CPL SE and a (validation) PPL ME at the same time.
Your student needs to get a FAA CPL ME add-on, then log the training for the MEI as PIC and dual received towards the 15 hrs requirement.
Not a big deal since here's a plan;
there is no requirement to fly the CPL ME checkride from the LH seat so it can be done from the RH seat.
So train you stduent fror teh ME add-on from teh RH seat as a practice run for his MEI.
Still need to do 15 hrs. after his CPL ME to meet the regs but you can use those to teach the finer points of how to stay alive as an MEI.
So your student has more RH seat time for his MEI check ride, makes sense?
To me it does but my brain died half an hour ago......
