This KSP mod adds a button in the Tracking Station to set a ship's orbit. If you are within 1% (configurable) of your target orbit, you can simply push the button to set the orbit's semimajor axis to exactly what you want, so it won't drift out of alignment as you time warp.
It's probably most useful for setting up relay networks, whether you need a single geosynchronous relay over the KSC or a network of four satellites with exactly the same period to provide constant coverage of the full surface of a planet.