There arent trusted ways to you to be able to make a stable income with your investment on such low time. You can try sport betting or trading some altcoins but make 0,50bt each month sound a bit hard really.
I agree with trading , you can earn profit for short till mid-term if you choose right coin you can earn 0.5 btc shortly , but you must have good knowledge and little of luck to choose the right coin to invest.
You are correct dude, much better if you will put it to invest in Any altcoin potential were you can do trading to grow your bitcoin/altcoins. Because if you know the skills technique in trading you can earn as much as 0.5btc and up in a day.