I think Dandy-Lion is wired so that every time he sees any sort of bonds/prison, his mind immediately begins to formulate escape strategies. Since this is inside the Brotherhood's HQ (essentially where Dandy-Lion grew up), he probably started thinking about escape strategies from the moment he first heard about/explored the Brotherhood's containment cells.
Come on, a secret society should know better. If you've captured Batman and plan to execute him, you don't tie him up. You break his arms and legs to make certain he can't escape no matter what bullshit skills he has.
Breaking his jaw then asking him to defend himself during the fake trial is optional.
