I use the windows Magnify app in lens mode and it works great. You can adjust its size and magnification. I'm using a Microsoft mouse with 8.1 and Magnify is one of the choices for the wheel when pressed as a button.
In windows 7 with a Wacom Intuous 4 tablet mouse Magnify is not a choice, but run/open is so I set it to run Magnify.exe in windows/system32. For some reason this would not work with the mouse but did work when assigned to one of the Intuous tablet buttons.
There was the occasion when it did not work in the CO2 window. Starting Magnify before starting CO2 worked and once inside CO2 I am able to turn Magnify on and off.
Obviously the best case is if you have a mouse that lets you assign magnify to a button.