What I did today is probably not so cool for the electrical engineers here...
Well, I'm and electrical engineer and your idea sounds pretty cool to me. I do not know how to read a .svg file (do you have something more accessible?) but I get the general idea.
I have found the PWM output a handy source of switching signal for voltage boost circuits, with the added bonus that you can start and stop boosting at will. Maybe you want to try flashing the backlight to get attention for an alarm condition.
Initially I intended to use a FET but then learned that the FET appears as a capacitor for the AVR output and might damage it.
If you are talking about FET gate capacitance, that is usually a very small value. Also, AVR outputs are relatively robust. There is a good chance the transistor has a base capacitance value as large as the FET's gate capacitance (drill down in your data sheets!) but it draws so much current the capacitance is considered negligible. With the FET, capacitance is all there is. The transistor is almost certainly a heavier load for the AVR output.