Quite easily. With Rafflecopter, it's possible to create a custom entry option by using the 'Invent Your Own Option!' entry option.
On the setup tab in your Rafflecopter dashboard, select the entry option 'Invent Your Own!', rename the title of the entry and add detailed directions for your entrants. If you're having folks enter a custom entry options, ask them to leave a bit of information so you're able to verify their entry when the giveaway is over. You can do that by clicking on the button that asks them for additional information.