I'm sorry truecrypt mounts under /media, not under /mnt as mentioned in my earlier post and no polkit authorization hacks required.
I installed truecrypt on this netbook with Mint 16 (Xfce) and changes to sudoers as you have tried works!
My entry in sudoers looks like this
where TRUECRYPT is a user alias to include all my usernames on this netbook.
This worked. Then I removed user alias line and put my username instead of TRUECRYPT, it still worked. I then put another user's username. This time I could not mount the truecrypt volume _as me_. But when I logged out and logged in as that other user, truecrypt mounting works just fine.
Don't know why it's not working for you. Just checking, did you exit truecrypt fully, launched again and tried? Also, I have 'never save history' checked.