i've heard that lemon juice in a spray bottle works because they hate the sour taste. also, petco has some things that you spray on what you don't want your dog to chew on, i wonder if that will work for the kitties.... also, put the glass ornaments on the top, they will be less likely to break. also, what i've tried is using a spray bottle with water and when you see one of them getting ready to take a leap at the tree, give a little spray. maybe you can condition them to not climb. it's possible. good luck!!! try to fasten the tree to the wall so they don't knock it down all together, one of mine did this last year!!!
ps the xmas tree article didn't really help me either... hope my ideas helped.