You can assign shortcuts to "Edit -> Special commands -> Zoom -> [In|Out|Reset]" with the keybinder plugin ("Settings -> Editor... -> Keyboard shortcuts").
Not all combinations are possible, e.g. "Ctrl" + "+" and "Ctrl" + "-", can not be assigned (don't ask me why, seems to be a bug in keybinder-plugin or in the way wxWidgets handles accelaration-keys.
Most touchpads are also able to simulate mouse-scrolling (mine does on windows and linux).