I have been trying to figure this out as well. I haven't been able to test this yet, but I came across someone yesterday saying that if you make a household with one adult, and the rest animals you want to be strays, then when you get to the town page to place them, you just hit the X to cancel placement, and the game supposedly then makes them homeless by default. Like I said, I haven't got onto my game to try it yet, but I thought I would pass it along.
BTW, I LOVE the idea of unique tester animals. I was just thinking I'd grab some tigers and pandas and such off the gallery, but your daughter's creations are soooo much better!