You say there's no food in the garage, but is there...

You say there's no food in the garage, but is there something nearby that they are feasting on - fallen fruit/produce, raiding a compost bin etc? You need to mix the rat poison with whatever they are accustomed to eating (or just use the food source in traps sans the bait), as they are very shy about taking unfamiliar food unless starving.

At my place, they scrounge around under olive trees. So I find that when I use fresh olives in the traps, it's a much higher success rate than using poison baits. They don't hesitate when there's a tasty olive in front of them.