With the system you're talking about setting up it wouldn't be possible to differentiate between a bell guard strike and body contact with the tip.

Why? Because in a standard epee setup with reels and the like you have one continuous circuit which is closed when the button on the tip of the weapon is pressed against any non-grounded surface.

In your system you would be fencing with two seperate circuits which wouldn't allow you to ground out the bell guard...

It still isn't such a bad idea though... considering the outrageous cost involved in purchasing reels, a machine and all the other toys... and it's easy enough to know when your weapon landed against the bell guard. Further, since you'd obviously be using this tool for training or for fun and not competitively, the honor system should suffice.