Some years ago, I suggested to add an option during install to select NetBeans UserDir and CacheDir [1]. This still seems to be an issue for other people. Take a look at the comments on my former blog post [2].

[1] https://netbeans.org/bugzilla/show_bug.cgi?id=221351

[2] http://blog.mueller-bruehl.de/reviews/select-netbeans-user-dir-during-installation/