Currently, Paint/Erase responds to Left-click with no Shift modified. Ctrl modifier is ignored. We could map some variant of the Paint effect to Ctrl+Left-click, or keep default 3D view behavior of Ctrl+Left-click.
Unfortunately, it is very hard to make small changes to keyboard shortcuts, as they would lead to a cascade of changes, ending up re-mapping a lot of shortcuts. It may be possible, but then we should come up with a complete re-map of all shortcuts that is accepted by most users.