I have the PI mountain bike booties in the largest size available and hate getting them on also. (Size 46 shoes) I had to bend a coat hanger into shape to get enough leverage to yank them on, it wasn't worth it.
Last winter I got Performance brand neoprene booties to replace the PI ones, and I love them. They fit snug, but because they can actually stretch, they're super easy to get on. They have a full rubber sole of their own unlike the PI booties though, which you just cut with a boxcutter to any size opening you want. I just cut them slightly larger than the recessed cleat area on my mountain shoes, and they do the trick. Due to the sole, it might actually make walking in your sidi's easier, too.
Link here:
http://www.performancebike.com/shop/...4&item=10-0082