So rather than shooting for a "controlled and verified" test, perhaps just taking a statistical sampling of the average success rate of TA traders versus the norm could be a reasonable test. Setting such a study up would require finding a large group of traders willing to be studied though.
You could test with play money to see how TA would work for investors not big enough to (significantly) affect the market. TA probably isn't as applicable to the big players anyway as they will be adopting more active strategies.