Yes, you can add more than one reward in simple way. You must add new reward to your original EXISTING reward that you pledged for. You can add as many of them as you like to your current pledge. To add an add-on, simply include the amount in the pledge.
Example: If you made a $63 ($53+$10 shipping) Super Early Bird pledge (Omnia Dress) and you want to add the one more Omnia Dress, simply, add $63 ($53+$10 shipping) (Super Early Bird) to your pledge and enter "$126" without changing the reward category.
After it, we will check your pledge , and after campaign ends, in the survey you will write your both rewards. In addition send us message via Kickstarter or leave a comment .