I just bake em but some comments on getting the liner into the shell. Get another person to place the liner on your foot, hold it nice and tight around your calf and then put on some (tight) panty hose over the whole shebang.
Then when you place the foot/liner combo into the shell, have your helper pull UP on the liner to prevent any wrinkles. The strategy I use is start sliding in your foot/liner with a friend pulling up on the liner the entire time, get the thing in but DONT put any pressure on your heel just stand on your forefoot. Have the helper again pull nice and hard on the liner, making sure everything is properly wrapped, when you drop your heel into shell. You can then hold onto the liner when your helper buckles you up starting from the 2nd, 3rd 4th/5th, then 1st