I would start by saying that I had to overcome a disability of my own (which is currently under control) so I can understand how you feel to a certain degree. Like you, I have not mentioned my condition to my employers and I did not seek any special treatment for GMAT. I knew for sure I did not want to come across as whiny in my applications, so I aimed to do well in the GMAT and then mentioned in my optional essay the steps I had taken to cope with and overcome my condition.
I agree with lsuguy - I think what the end goal you should strive for is to demonstrate to adcom that you can handle the rigour of an MBA program if admitted. In fact, I believe there are scholarships out there for individuals with disabilities.
If you want a better score I think you can do it, just commit yourself to doing better instead of writing an essay about how you can't do well. Don't have things handed to you because you can, overcome the odds and get that 700+ score despite your learning disability and prove to everyone you are a person who will overcome any odds to be successful (now that's an essay)