I've never had this problem and I feed frozen-thawed most of all. I'd switch to other brands, or other frozen foods, or prewash the prawns well for your RTC, as simple as that. I hope you are aware of the thiaminase issues with crustacean-rich diets.
I do recall a thread or two where hobbyists stated that their large predators ignored small prey. IDK how spread this phenomenon is. Judging from the scarcity of such reports, cases like these appear exceptional, although it may simply mean that few people even think of that.
I also recall some keepers report that a fraction of their live feeders does not get eaten and hangs around the tank and even grows up.
Having said that, I think the risk is way too high your clean-up crew, fish or ghost shrimp or snails etc., will be eaten up.