Let's see... given your current drive-axles are about one foot long, each... and less than an inch in diameter... a carbon fiber mod should save you... five pounds.

Some RWD cars get a carbon fiber driveshaft, but I've never heard of anyone doing carbon fiber drive-axles... for parts that small, I don't think the carbon weave can take the stress. Drive-axles are puny little things. Hell, I've snapped one or two. They're not like driveshafts, which are large, heavy tubes running underneath the car.

Like GH says, go get cosmetic CF, instead.