It really is not that easy. Even if you are willing to pay for a proctor, it is not unusual for the answer to be no. This is a source of serious contention for homeschoolers every spring. I had a difficult time finding a school to agree to let my 11th grader sit in for the PSAT. A private school finally agreed.
When CB controls the tests, it seems illogical to not have testing centers which provide equal access similar to SAT and ACT. But, access is up to individual schools. Some districts are more friendly than others.