Naga Pro Mouse button for Windows Task View (win+tab)

I'm trying to map one of the buttons on my Naga Pro to the Windows Task View. There isn't a dedicated shortcut for this under Windows Shortcuts (Task Manager is not the same as Task View) and when I try to map a keyboard function, it won't recognize the Win key as a modifier. How do I map win+tab to my mouse buttons? For that matter, I'd also like to map Win+Ctrl+left and Win+Ctrl+right to navigate virtual desktops.