I amsurprised its growing with just an incadescent. Buy a book and read up check out the site for compact flouro light (CFL) info and grows, thats gonna be your cheapest option or you canget yourself a metal halide light or High pressure sodium. These produce more light and will help keep your plants shorter. Also learn about topping and low stress training to keep themshort.
At 2.5 feet its gonna be hard to do anything since the plant is established already these methods are best to start early. I would do what I said and take cut of the plant and put them under CFLs or regular floros until they root and have many smaller plants to deal with.