I don't see how that games the system though. The guy who leaves loses LP, and his friends gain nothing (At the end of the day, they just waste their own time). Good luck asking your friend to throw away his LP to be the one to leave the game, I don't think I know anyone who would be willing to do that.
I mean, if I duo'd with a guy who's power went out because of a storm, I wouldn't want to be the only other person to lose LP for that. It wasn't malicious. The guy I duo'd with should not have queued up if he knew a storm was coming and that storms had a history of knocking out his power (And thus should lose LP) :P
I think losing double LP is too rough of a consequence especially for the storm scenario I just mentioned. Again, it wasn't a malicious intention. A compromise could be to make it affect their MMR as well as losing LP. If they knew they would lose more LP for future losses, and gain less LP for future wins, I can't see anyone ever disconnecting just so they don't have to finish a game they're losing early.