I've personally only seen pasty butt in shipped chicks. I assume it's a stressful process, and the lack of food and water up front is a bit hard on some.
We're yours shipped?
I've read of people using a Q-tip to apply the oil. I do understand working with tiny bantams. Make sure your brooder isn't too warm, sometimes that can lead to pasty butt.
I generally just clean their bums as necessary. I have read a bit of olive oil can help, but I haven't done it personally. Most pasty butt stops by the end of the first week.