Ball screw lubrication question

A have lube points on everything but the Z axis ball screw on my BP.
I'm using the original retrofit that came with the machine and can't
figure a resonable way to get automatic lube to it. Its also a
disassembly job to get to, so I'd like to figure a way to lube it and
forget it for a while (and also know when to relube). What should I
use as a lubricant? The nut seems to be pretty sealed. Where/how do
I lubricate this? How long should the lubrication last?

Thanks much,
Jeff