Something like a Meet the Spy type of sapper, where you can throw it, and if it hits a sentry, it will attach itself. It will take maybe 5 seconds to attach, where it can be destroyed, but if not, then the sentry will attack engineer's team. The downsides are that the sentry will only attack its team for 3 seconds after it gets sapped, and it doesn't do any damage to the sentry- like the red tape recorder.