How can I cut a notch in a glass shelf?

I am installing my fitted kitchen myself and have come up against a minor problem. I have fitted a cupboard over 2 water pipes and cut a recess through the back so it fits nicely against the wall. Unfortunately the shelf inside is glass and wont fit all the way inside as it touches the pipes. This means the door won’t shut properly.

How can I recess the glass shelf to allow for the pipes (only about 5mm)so it will go all the way in.