There is no such thing as risk-free.
Well, US Dollars in banks, at balances below 250,000, those could be considered risk free, and up until the financial crisis, you used to earn some interest on your deposits as well.
The way that banks produce interest to credit to your account is by loaning out your money; the money doesn't just magically multiply while its in their vaults.
There is, so far, no equivalent in the Bitcoin world.
Moreso, and more importantly, any offers of "risk free" ways to invest your bitcoins are likely scams. If it means sending your bitcoins to someone else, you have to trust that no only will they pay you interest as promised, but that they will actually return your bitcoins as well. Because if they don't return your coins, there's no way that you can force them to do so.
My advice: Hold onto your coins. Don't get greedy trying to earn something from them, because that just opens you up to so many of the scammers that have operated with near impunity for way too long. And know, even if you find an investment with great reviews (people who invested, earned something from their investment, and then got their money back), in too many cases these have been ponzi-schemes. Just because someone who invested before you got their money back means nothing for getting your own money back...
And, as I actually blogged about, even the most trusted names in the Bitcoin community can suddenly "go bad"... Friedcat, for instance, was an anonymous person out of China that launched ASICMINER, and for a couple of years proved to be a trustworthy steward of his clients investment. Then he launched AMHASH, a cloud mining service, and in just a short time disappeared with his investors dividends, and quite possibly the hardware as well.
Story:
http://www.btcreporter.com/2015/03/04/mystery-in-bitcoinland-the-disappearance-of-friedcat/So again. Hold your bitcoins and be safe. The world of Bitcoin investments is basically the wildwest right now, and you're far more likely to lose it all than you are to earn a small return on your coins.