You may want to have a look at IOMAD, that might offer a better solution than anything else you are likely to try.
AFAIK, there is nothing that allows you to do that, as such, BUT..
If you create a Category for each organization, assign Admins at that level, have a series of meta courses with the child courses in the Category, that MIGHT go a way to solving your problem. I've never tried anything like this, so there is any number of issues that will likely prevent it from working, e.g. a child course may not connect to any parent course not in the same Category, never tried it, but it is interesting. A Category Admin may not be able to add a User to the site database, even though they have full rights in that Category. Something else I've never thought of or tried before. Never know, might work, but IOMAD is worth checking out.