I haven't attached it to a flying saucer yet. I'm thinking for a FS you may want to invest a little more and get a wireless version of the odometer. That way you won't have a cable to deal with, and will have more options for the magnet/sensor placement.
However, I’m thinking if you attach the sensor at the front of the base with handi-tak and the magnet to the underside of the saucer it should register. If you use a wired version of the odometer there may be room on the back of the base to attach it with handi-tak. You will have to play with it, and if you do get it to work, you absolutely must post an image and tell us how you did it!