I disagree with forcing users to click the install button.
A better suggestion IMO would be to show a notice at the top of a mod thread when you downloaded it, but you didn't click the install button. Something in the same style as the rating notice. This shouldn't be very difficult to code.
It could also include (a link to) some information about the install button (show appreciation, update notifications, ...). At the moment there's no
info page about it. This could be useful for new users.