The obvious choice is to choose a support that can carry. Since you're not keen with that option, I'll give you what I can.
Disclaimer: I only haunt the boards. I haven't played since October, so things may have changed. End disclaimer.
-Support your best ally. That's the best bet, as it will afford the best use of your skills to support the team. If your carry has become cannon fodder, that means it's time to go.
-Build accordingly. Your income is based off of whatever your support item's conditions are, so make sure you get as much gold from that as you can. Since meeting the conditions oftentimes requires a partner to do decent, your wallet is gonna be light, so make sure you prioritize your build carefully.
-My main support was Lulu. If you go ghost, flash, and a lot of Mana regen and cdr, you can run around the map and make your opponents chase you for long periods of time. It's kinda trolly, but it can be helpful (and hilarious) to keep some of the tougher enemies busy on fruitless endeavors for long periods of time. The trick here, however, is not only being able to remain elusive, but also to remain tempting enough to chase. Try to practice if you're interested.
-If you're loaded with CC instead of power, you can at least cripple your opponents. Your team will at least have a better chance if your heavier opponents have to lose a couple seconds due to a silence or a stun. If you can chain CC, bonus points.
-If you're so pressed out of luck, sometimes, you just gotta start farming and building up the damage. Better for you to take the driver's seat instead of someone who can't drive very well. It may not sound like a good plan, but you're doomed to lose anyway. Might as well try to shoot the moon instead of just staring at it