If you can rig some sort of container above the display you can do a gravity feed through a mechanical float switch with some tubing & a few fittings. That way there's no electricity involved & one less failure scenario. The trick will be finding a small enough mechanical float switch that it won't be too intrusive in such a small display.
However you end up doing it be advised that there's not much room for error with a pico, so test it well before taking off on a holiday. Even then, have someone look in on the tank every day. Limit the size of your top up container so that the results of a failure aren't too disastrous.
I use a pressurized glass wine carboy for ATO on my 77 gal. Post #24 in the following thread shows the set up.
http://www.canreef.com/vbulletin/sho...&highlight=ATO