I did it on my old vectra b, it is a lot of hassle. It involved cutting the flip key casing in half and a bit of modifying the original remote internals to fit inside the flip key case. I worked in a factory at the time and had access to plenty of tools and precision equipment like grinding wheels and drills. I managed to do it with no bother but the casing looked a bit messy after gluing it back together and it eventually fell apart. So i'd say it's not worth it.