In every investments, you need to have a capital, it is seldom to trade without investing any amount. But there is a way to trade without any spending, best example is participating bounty campaign where you were received tokens as a reward then you may now trade it.
I think it can be done, but it takes a long time to get big capital you need other capital than bounty. To trade requires a large amount of capital, if not then the profit received will not be proportional to the risk.