Richard,

Can you assign different conductivities to different wires in EZNEC? I
don't think you can.

You could distribute the resistance, 1 load per segment each having a
resistance of 1/#segments of the total. It seems important for
coupling to have a realistic diameter (fat) wire for the carbon fiber
pole, but it needs to be lossy.

A load taper from bottom (large tubing, lower resistance) to top (small
tubing, high resistance) would be easy to implement as well. This is
probably only worth it if it seems that the loss will be nonnegligible,
but it could take into account the effect of the element current
distribution on loss.

Dan