Your lever is not ruining the cable, chances are you've had a bad cable all along.

Use one of these http://www.performancebike.com/bikes...:referralID=NA

I've been running those cables on everything I own and they are bad-ass, pre stretched and teflon coated so the metal isn't exposed to water so they won't rust. Website says $15 but they're always on sale for less than $7 per cable.