How could I lengthen my lateral incisors? (photo)

I used to have a very large gap in my teeth which was corrected with braces. I had permanent retainers put between the two central incisors which broke and therefore made my teeth more crooked. But that's not really the issue I'm concerned about. Because my teeth were gapped, there wasn't a lot of room for the lateral incisors, making them very small. What would be the most economical and effective procedure to make them more uniform?