I finally was able to change the rear brakes on my V40. As anyone who has tried this knows it is difficult. You have to turn the piston clockwise while compressing it. Just compressing or just turning will not do. I had tried the "cube" tool to turn it, but I couldn't compress at the same time. Finally the solution was tool OEM #27111 from Autozone. They have a free rental program. You pay $35.00 for the tool and then either keep it or return it for a free refund. The tool has several adapters that fit into different pistons. Once I had the caliper out I was able to quickly identify the adapter I needed and fit it into place. It was a little tricky to get everything in place (couple tries, couple minutes), but once I did the piston retracted easily.

I had to call several Autozones to find one that had the tool in stock, they seem to go quickly. Let me know if you have any questions.