He knew the salary when he ran for office. If it wasn't enough money he shouldn't have run. If he needs to moonlight then he must resign. If he insists on going ahead then he should be removed from office.
I am appalled that anyone would try a stunt like this. The fact that Gessler is a licensed attorney means that there are professional ethics rules which will complicate his plan.
Update: I went through the rules concerning Conflict's of Interest and posted about them above.