Carefully slip the ribbon cable in as far as it will go and then either use a small piece of foam, sandwitched between the LCD and the ribbon cable. There should be enough pressure once the LCD is in place to keep the ribbon cable in place.
You can also drip some hot wax on the connection. Once the wax hardens ( 5-10 seconds) it will keep the ribbon cable in place. Dont use alot of wax, just a drop will do. Whatever you do, DO NOT USE SUPER GLUE!!