AhRT Cosmetics has a way to do it. They made three lotions – one for slimming, one for moisturizing, and one for refreshing effects. The lotions, which contain hemp oil, caffeine or menthol are to be used during machine or hand washing as if they were mere fabric softeners, and the technology that makes it work is called micro-encapsulation.
Micro-encapsulation is a process in which tiny active particles or droplets are surrounded by a coating, in this case a silicone coating, that allow them to spread around when the coating is crushed, during the contact between clothes and the skin, for instance.
Think its worth a try?