I think one things which would make this idea feasible is the fact that people are old by the time they receive SS so a certain percentage (a somewhat predictable one) will be dead. If a high enough percentage is expected to be dead, you could create rates which would allow you to win over the long run.
You could also make the SS insurance apply only to the individuals and not their beneficiaries who would have received the SS benefit in the event of the individual dying prior to receiving benefits.
I know it's grim but just some thoughts..
They could also figure out financial consequences of social security going away and place long term bets on that. If they are able to hedge properly, they're basically reselling that hedge.
You need to find someone to take the other end of the bet. So, who would want to insure themselves in the case where social security stays around? Can you find enough of these people to balance out your risk?
Well I think it probably will be around. Most big (popular?) government programs aren't going away no matter what the media says.
So how about selling social security insurance. Buyers pay a premium each month to buy the insurance. And if social security isn't around when they retire the insurance pays out what they would have gotten from social security.
---- Edit ---
People don't think the insurance idea is viable so let's turn this idea on its head. The company goes out and buys the future social security benefits (or some portion thereof) from individuals ands pays them say 10 cents on the dollar. People who don't think SS will be around think they're getting free money, and the company makes a bundle if SS stays around.
Heck, could the US government could be doing this to fix social security?