Why can't you resize the Windows Environment Variable box?
I'm going to blow your mind here, but as of Windows 10 build 10565, this window is finally resizeable.
https://plus.google.com/+ArtemRussakovskii/posts/h1En1s5abJs
Maybe you'd like this nifty tool I've been using for a while, ResizeEnable. It allows you to resize windows that are normally not resizable:
