I'm not sure what you are getting at. Migrants are currently technically "sneaking in" at a very specific location. By funneling them to an official border crossing, they can be immediately turned away using the safe 3rd country rule.

Unlike the people who came in the winter across farmers' fields further west, these people are arriving in taxis with children and dragging luggage, and so are far less likely to be able to truly sneak in.

Yes, this could end up being a whack-a-mole situation, but quickly sending a few migrants back sends a message.