Can you put the leash on her earlier, and let her just drag it around in the house for an hour or so? She may get tangled on furniture legs, so you will have to watch to deal with that.

You could also put the leash on, take it off and treat, then go do something. Do this several times over the 2 to 3 hours prior to the final walk, so she never knows which one is "the" one.