If we assume the courts can order you to decrypt the drive (and without debating that point) - one has to consider that the court may be fully aware that the system has multiple hidden volumes, either by eyewitness testimony, 3rd party evidence (check out truecrypt's warnings on their site about full system encryption and what to watch out for. Things like finding the same windows installation doing every update twice. There are all kinds of information leaks that COULD pop up.
I'm not saying it's impossible - just as strong cryptography, which is easy and is all over, doesn't mean all our data is secure, neither would a more complex system like this protect someone from the legal system.
You can use one algorithm to encrypt/decrypt the original content. But you can use a different algorithm (with a different key) that would output a different output.
The secondary algorithm would be one that given a some text (ciphertext from the original encryption) along with the desired output, would return a suitable key. The most basic example to prove the point would be XOR.
If you give a password, the cops will know what algorithm they must use (2 trials at most). Even if they don't know before hand which algorithm points to the real data, they can notice that it doesn't use all data.
With your method, you can at best cast doubt: is the data not extracted real data encrypted differently (algorithm or key), or random data that the software insert by default to give everyone plausible deniability?