Sorry i was assuming you had the pc's set to shut down immediately when the power goes off. I expect a capacitor could be used to delay switch off but it wouldn't be intelligent like the ups software.
You could plug the ups into a old pc and when that turns off (stops drawing power) the rest will recieve a shutdown signal via the motherboard PWR_ON connector. The only problems with that are you need a master pc to tell the others what to do and if that pc fails for some reason everything will get switched off. You could connect your thermostat to that pc aswell so everything gets turned off when it gets too hot.
You could plug the ups into a old pc and when that turns off (stops drawing power) the rest will recieve a shutdown signal via the motherboard PWR_ON connector. The only problems with that are you need a master pc to tell the others what to do and if that pc fails for some reason everything will get switched off. You could connect your thermostat to that pc aswell so everything gets turned off when it gets too hot.