There are actually NO crepe myrtles that are completely wood hardy in zone 5, but they are root hardy with a good mulch, and provided adequate heat and sunlight, there should be no problem with some of the hardier varieties dying to the ground and regrowing 6ft (at least) in a season and blooming from July to October. Some of the hardier varieties are crosses of the common "southern" L. indica and L. faurei (sp?). They can usually be idenified with their typical "Indian" names. ex. Hopi, Tonto, Zuni...
All of which I grow here in N.E. Ohio with success, although bloom is never as good as further south due to the lack of heat along Lake Erie, which should not be a problem in Kansas. By the way, I think Kansas is more borderline zones 5/6. Also supposedly a cultivar named "Velma's Royal Delight" which originated in Kansas is very hardy. I have seen it sold in the Cincinnati/Dayton area and is a "purplish" color.