Assuming you can't use leverage, derivatives etc, you should put 100% in a single highly volatile stock. You probably won't win, but the winner probably will use this strategy. You're not trying to give yourself a secure retirement income, you're trying to make massive gains in a short period of time. Fundamentals are irrelevant. Diversification will just dilute your gains if you do hit the jackpot. In this game, there is only one winner - a sustainable positive return is no better than crashing out and losing everything.
Look for things like small pharmaceutical companies, small mining/energy companies, small tech companies with big hype. If it's got momentum and a good story and looks a lot like a lottery ticket, it's what you want. You'll probably fail horribly, but no sensible investment is going to double in three months. When it's mostly hot air, the price can go anywhere.