Oil lines as electrical ground return?

I accidently wrote my first post as a reply to another thread, so here
it is again on its own.

I have a pusher airplane with a nose oil cooler.

I am replacing the existing heavy hydraulic type(rubber/braided steel)
oil cooler lines with lighter metal lines. Either soft Aluminum or soft
copper 1/2 lines.

First question. I would like to use the lines as my ground return and
remove the 2 AWG wire I have now. Good idea?

Second question. Which would be better, or possibly which would be
worse and why? Copper or Aluminum.. Aluminum would be lighter but
copper offers a better ground return(less resistance). I have a big
engine and the starter needs all the current I can muster.

Scott