I leave offerings. A plate of kibble on the back porch usually does it. I've had several cats wander through my back yard in the time I've lived here. One I took in, looked at missing cat ads on Craigslist and got him to his owners. Another I took in and kept. There's a grey cat who visits almost daily, but he's feral and won't let me near him.
The fact that I've got the only dog-free yard in the neighborhood probably helps.
To make it a spell or ritual, when I set the kibble down I'd make a prayer to Bast to let stray kitties know that they're welcome here and that they'll be safe and fed.