Magic Mouse scroll-zoom without keyboard

Hi. My last mighty mouse has died, and I can't find a way to get my magic mouse to scroll-zoom one-handed (with no need to hold a keyboard modifier key). With the mighty mouse, I could right click and hold with my middle finger to simulate holding the control key down on my keyboard while scrolling with my index finger to achieve a smooth zoom in or out. If I assign the appropriate universal access modifier key to any action in MagicPrefs, simultaneously scrolling while holding the modifier key action results only in normal scrolling, not scroll-zoom as with the mighty mouse. Has anyone figured a way to smoothly scroll-zoom without having to hold a keyboard modifier key? Alternatively, is there a way to smoothly zoom in and out using any of the assignable gestures in MagicPrefs? Zoom in is always a big increment and zoom out is in smaller increments as it stands, which is almost useless for my purposes. Thank you for your help.