Another tip that has worked well for me is waiting for the sun to get on that part/side of the liner. Once warmed, it's very pliable and can just use your fingers to pull up into lip and get it seated on bead. With the liner in the shade, even on a super hot day, it was very difficult. So really the key is to warm it up a bit so it's more pliable.
I'm too paranoid to use any kind of tool.