Adding a waistband

I just finished my first pair of Field Trip pants this weekend, and I love them! They do illustrate why I should go through the effort of pinning down my (seriously unwilling) model to actually get his measurements, as they're a good two inches too long, but I love them anyway, and they'll fit him eventually. I love these pants so much I finally actually posted in the Flickr group. I want to make him a pair that fits now, though, and while I'm at it, I'd like to add a waistband, as opposed to the facing/topstitching combo that's there. Can I simply use one from another pattern (Sketchbook? Art Museum? Sunny Day?), removing the finished waistband width (minus a seam allowance) from the top of the pants back, front and pocket pieces? If it makes a difference, I plan to omit the belt loops, since I never put a belt on my toddler.