Collapsible categories in write page

I have been looking and looking for a solution on how to make categories in the write page show as collapsible categories. I see there are what seem to be thousands of options to do this in the sidebar but not the write page. I have 500 categories and growing. This is very clumsy for an user to have to scroll through that many categories. I want the user to pick a parent category and then that will expand and so forth. Most of my categories are children so this would greatly reduce the clutter on the write page for a poster. Please let me know if anybody out there has a solution for this, it is keeping me from moving forward with my blog!