how about simply buying bitcoins and storing them offline in a secure manner.
that's how simple investing in bitcoin is.
i agree, this is the best and easiest way for people who either don't know how to trade or don't want to trade on regular basis on each price change.
and it is good to keep in mind that buying at any price is not a good idea. buying must happen in the lowest price possible even for long term investment.
the only problem with buying when the price is at its lowest is that no one knows where the bottom is.
currently it is quite safe to assume that at $300 it will be considered a solid long term investment.