JPM,
How about the 'Mouse - Properties' object itself?
My IBM/Lennove ProPoint (the one with the directional button in-between the keys) shows a 'Scrolling' tab in the Properties where you control how your mouse hardware use is to be mapped to inputs.
There is also the 'Mappings' tab, which further defines options for things such as MB3, etc...but that is a XWP feature.
I haven't found anything in Lotus 1-2-3 that actually allows you to further define mouse actions.