Desi, I know your enjoying it but I think your giving Rich a bit of concern when none is warranted.
Desi, there is nothing connecting the positive terminal to the frame or the battery unless the key is turned on. In other words, there is no way you can get a shock by messing with the negative terminal, connected or disconnected.
Your idea with installing a bolt thru the wiring connector and the two holes and securing it all with a nut is the way to go. It is probably what was intended in the first place and whoever put the battery in before you got it did a half ass attempt to make up for not having the right screw and nut. Shame on them.
Use the screw and nut and do it right.