You could use rebalancing, which means you always have 50:50 in Bitcoin and USD. It isn't a very useful method for generating money, but makes risk aversity an option.
Basically: Bitcoins rise, you sell, Bitcoins go to valley, you buy. Trying to keep the ratio right.
Just for kicks I analyzed what would happen if you started with $100 2 years ago and rebalanced daily. The price was $3.5 then, which would give you 15.344 btc after 0.5% fees. Today you would have $478.80 and 3.546 BTC, for a total value of $957.60. If you kept the $50 and equivalent BTCs the total value would be $2121, which includes about $40 in saved fees.