The closest thing to a sugar pill available is known-bad advice, and giving known-bad advice to a control group strikes me as decidedly unethical.

It would seem ethically acceptable to give groups advice selected from common social norms. For example, give one group some "Getting Things Done", another group nothing at all, a third some instruction on calculus (irrelevant but still high status attention and education), a fifth a drill sergeant motivational yelling at and the fourth group gets PJEby's system.