This is the trickiest part of the job. Cutting the hide along the tail to extract the tail isn't acceptable. Leaving part of the tail inside the hide is also unacceptable. I don't even know the name of the tool or where to point you for getting one. Find a hunting chat board and ask there.
Someone is bound to have a name and or number for a tool.
Continue skinning, creating a hide 'tube'. Do the same for the head, You can leave the ear cartilage in the hide but no flesh or fat. Skin the ears out far enough to insure that the only material remaining is cartilage. Skin out everything down to the yote's nose. You can leave a small portion of nose cartilage.