How to change external display resolution WITHOUT clicking "CONFIRM"?

I have a somewhat unusual situation. My MacBook laptop is actually now a ModBook (a pen-tablet computer), and as such I no longer have a trackpad attached to it. All of my inputs are via the stylus, tapping directly on the built-in display.

This works perfectly fine, except when I need to give presentations on an LCD projector (which is quite often lately). I like to use the projector as an external monitor, so that I can run the Keynote presentation on it while using my laptop screen as the presenter's display, with the upcoming slide, etc. If the projector doesn't give me an ideal native display option (sometimes, the aspect ratio for the 3 or 4 resolutions available in the Displays drop-down in the menubar turn out to be stretched or squeezed), then I, naturally, have to open the Display System Preferences and try out different resolutions.

The problem is, since my stylus only interacts by clicking directly on the built-in-display, I have no way of moving the cursor over to the external display when the dialog box with the "Click here to confirm change/You have 15 seconds..." message appears. So I can never click it ... so I can never confirm the new settings.

The workarounds I've used so far are:

- Mirror displays (not ideal, as I need the presenter preview of the next slide)

- borrow a mouse from someone (usually from a Windows desktop, frankly) and plug that in to briefly mouse over and click the confirm button

I'd love to find a software workaround that allows me to NOT mirror displays and also doesn't require me to carry around a mouse all the time (my laptop bag is already overstuffed...).

Thanks.