Although TrueCrypt hidden volumes may have some practical applications, we think they are unlikely to be useful in the border search context because they are most helpful when lying to someone about whether there is additional hidden data on a disk. Lying to border agents is not advisable, because it can be a serious crime. [PDF: https://www.eff.org/sites/default/files/filenode/EFF-border-...]
Might hidden volumes help you pass a cursory check? Sure. But if someone really wants your data it's not likely going to keep you out of a contempt of court charge.
Now all that you have to do is prove that you either don't know or have forgotten the key that decrypts your random bits into a plan they will accept. How hard do you think it will be to convince an aggressive prosecutor/judge that you are innocent when you have no evidence (can't prove a negative) and the government has reasonable suspicion?