I like your theory. Unfortunately, I know for a fact that I've seen Tim (and I think Dick at one point) cross-dress better than that. Tim on the undercover mission where he's dressed as a (female) medical student, and I believe it was Dick who once dressed as Babs!Batgirl so she and her alter-ego could appear together in front of her dad. But that being Tim in bad drag would make more sense than that being Cass.