I imagine you could wind a piece of bare wire around the PVC pipe, sort of
in a wide spiral with lots of room between the turns, as a way to collect
the charge from the surface of the pipe.  I am guessing that these "radiant
energy" collectors being described are collecting the static charge from
the insulation, but they require the charge to pass through
the insulation which might be reducing performance.  I would guess that
the strongest static charge would really be on the surface of the insulator
so it would be best to collect it from there.  Also, the use of a big
(4" diameter or so) pipe would give the wind lots of surface area to work
on.

Perhaps, though, the bare wire on the outside would interfere with the static
collection by returning some charge to the air.  So, maybe you'd need to
coat it with an insulator or bury it slightly in the PVC by using some
glue to dissolve the surface just below the wire.