About all you can do at home is to drain and capture the coolant as much as you can (pull a hose and blow through the heater to help expel coolant trapped in it); then fill with plain water and do it again. By then the glycol concentration should be too low to worry about and you can go ahead with the flush. Any spillage will be further diluted by the flushing process, and you can wash it down the drain or into the yard afterwards. Glycol bio-degrades quickly; in fact it's major danger as a pollutant is that it degrades so quickly it can use up the available oxygen in the water.
Other option is to take it to a radiator shop.
FWIW, my own observation has been that cats seem uninterested in coolant. They might drink it if nothing else was available, but the alley cat that was hanging around my garage didn't even sniff at it.