Well, if you added sulfites and sorbates, you could add about anything to sweeten it up (sugar, artificial sweetener, lactose, etc), and since you have it kegged, there aren't issues you would have with bottling.
Just an FYI for next time, make some graff instead. My first ciders came out wicked tart until i started adding a little malt and hops. Now they are just friggin awesome. I am still awestruck at the difference. I am sitting her sipping one tonight that I just kegged -- it's still warm and flat, and i still love it.