Try telling your client this from the '14 NEC (411.4(b))
(B) Assembly of Listed Parts. A lighting system assembled
from the following listed parts shall be permitted:
(1) Low-voltage luminaires
(2) Low-voltage luminaire power supply
(3) Low-voltage luminaire fittings
(4) Cord (secondary circuit) for which the luminaires and
power supply are listed for use
(5) Cable, conductors in conduit, or other fixed wiring
method for the secondary circuit
The luminaires, power supply, and luminaire fittings
(including the exposed bare conductors) of an exposed bare
conductor lighting system shall be listed for use as part of
the same identified lighting system
Number (4) is specific!
