I've had some luck "streching" my MLC shoulder bells. All I did was to warm the item up gradually with water until you are using straight hot water. As I held the item under the tap I gently streched the item to my desired shape. At the point I was happy with them I switched to cold water and "reset" them.
I had to repeat a couple of times but the shape has held just fine.
Knees are more delicate than bells though so be careful.