That is a myth. Nearly all of the big BP breeders and members on this site feed their BP's in the snakes cage. A BP isn't going to get aggressive or think your hand is food because of this.
You need to clean/disinfect your cage at least monthly anyway (as well as change your substrate). A good way to do this is with vetrinary grade disinfectants like F10 and Chlorhexidine:
http://www.reptilebasics.com/cleaning-products