How to keep an outdoor rabbit cool in the summer?

My mom let me adopt a rabbit 2 or 3 years ago, as long as I kept it outside during the summer. I did not know when we got him that rabbits can die of heatstroke in temp.s 80 degrees and up. It's going to be in the 80's all week. I tried explaining this to her, and all she says is to keep him in the shade. Last summer I kept switching frozen water bottles in and out of his hutch, but he's been in the air conditioning so far this summer and I don't want to put him in the heat. What can I do?