Through my job at Meijer, I have taken great pains to study people. Both the people who shop there, and the people who work there. Here are some of the results.
As a cashier, if you want to avoid customers, the easiest way is simply to hide in plane sight. Rather than look to the lane lights to see which registers are open, customers look for cashiers at their register. So, if there are no customers in my lane, I like to go to the next lane over and bag for the cashier there. Or I'll go stand at the end of my lane which, if it isn't busy, is what we're supposed to do. As long as you don't make eye contact with the customer, they usually just pass you by.
As a customer, if you have a specific cashier in mind that you want to process your order, make a note of which lane they're own when you come in. When you finish with your shopping, look down the rows to make sure that their light is on. If it is, head straight to that lane, do not look cashiers who are standing at the end of their lane in the eye, and you won't have to say no to them when they ask if you're ready to check out.
For some odd reason, as long as you don't make eye contact, people tend to ignore you.