That's not nice, not at all. You are talking about intercepting mouse actions that aren;t intended for your form, and that's not the way it's all supposed to work.
As a result, it's difficult. Very difficult. And also dangerous...
You can do it, but you need a Global Hook:
Global Windows Hooks[
^]
Be aware: if you get it wrong - even slightly - you can render your whole system unstable and may "cause data loss".
Think twice before you do this: you will probably have to reboot your PC quite a few times in development, and I'd recommend an even more rigorous routine of backups than I normally would (and this from someone whose system does incrementals
every hour...