The installer presents the end-user license agreement (EULA). Immediately following it, it presents a multiple-choice quiz that asks questions about core parts of the EULA, such as permissible use, cancellation, refunds, jurisdiction/arbitration.
The installer then contains all the files to be installed. They are encrypted with a key that is composed of a hash value of the correct answers to the above quiz.
In this way, you could tie together whether someone reads the EULA with the possibility of performing the installation at all. This, in turn, causes successful installation to act as implicit proof of having read the terms. The order of the values must be randomized to prevent transmission of correct answers by index number only.
You are at home, and want to go shopping.
Your door only lets you out if you correctly answer some questions about the most recent changes in the law of your state.
Are you not a lawyer? Well tough luck, order your groceries trough Amazon then..
― Philip K. Dick, Ubik
However, your idea of an installer is novel. The problem is that it adds friction to the install process than would turn many users away.
I did for a while in the beginning but now its just too much.