Why try it: If you couldn't really care less what your bridesmaids are wearing, as long as they look good!
How to make it happen: You might get some confused responses from your bridesmaids, as this dressing technique is definitely not the norm at weddings. Let them know you want them to pick a dress that they love, and that's that.
However, you might find that your bridesmaids want more guidance. Give them the wedding's dress code up front, and also tell them what the wedding colors are or what the theme is. A whimsical barn wedding is very different from an old Hollywood glammed-up affair. Feel free to also ask that their dress includes, for instance, the color blue to add some level of consistency among the bridal party.