[On using CGI in Batman Begins] "I think there's a vague sense out there that movies are becoming more and more unreal, I know I've felt it. The demand we put on ourselves was to be as spectacular as possible, but not depend on computer graphics to do it."
The Limited Use of CGI in “Batman Begins": While Nolan tried to keep everything in camera, a few scenes weren’t possible to do without a little help from CGI. At one point in the movie, Bale’s surrounded by thousands of bats. Nolan acknowledges he had to use CGI in that scene. “Yeah, well absolutely but we did shoot real bats as well. I mean what I’ve been saying is we shot - for everything that appears as a visual effect in this film we shot material to base it on, whether in the form of a stunt or photographing buildings and what have you or miniature photography. In the case of the bats we shot a lot of tests with real bats and some of that footage is in the film where you see close-ups of bats. They’re real, but then to multiply them out to thousands upon thousands that was CG, yeah.”
He tries his best not to use it. That was part of why Begins was so expensive, because he wanted to do everything the real, old-school way. Either way, he's certainly not going to use if in this scenario.
EDIT: That and we've already seen Heath in full Joker makeup. With green hair.