0.1 BTC is too little to even consider any kind of investment, what you should do is look for ways to earn more bitcoin, signature campaigns, offering your skills to the community for bitcoin or get a job, earn fiat and buy bitcoin with it.
It's not small, it's big enough, in fact you can use it to buy altcoins that are blooming today...He might earn bigger that way if he is good at seeing which altcoin has a future and which one will be a shitcoin... But as to make his/her investment larger, I think you are right, he/she should be looking for some ways to earn more bitcoin...
