i have never seen this arrangement, but i'm sure you could have a farmer john or full suit midified at pretty much any dive shop. this arrangement will leave your torso exposed and in the event you wind up in cold water, could cause problems. if the object is simply to keep your legs dry, you might check out the henri lloyd anaconda pants. i think gill also has a similar item.

if you let us know exactly what you wish to accomplish, someone might know of a readily available solution.