What if you invest in yourself ? Or a business you know ? Bitcoin investments dont really exist because bitcoin is so volatile I guess.
You can count altcoins as investments too. Gambling is much better then HYIP though.
There are gambling sites with investment feature, you can invest as low as 10 mBTC. you won't profit much though if you invest low amount, the bigger amount you invest the bigger profit you'll make.
But he have to be cautious about the benefiting sites and about losing sites. I am saying about the sites which have a good reputation in the community and where a large number of people are gambling on these sites you will earn while on sites which do not have gamblers will not make you earn.