Okay this idea is dumb but I would love to see it done: As Kepler goes around the Sun (no, not the Earth, the Sun), it is sometimes flying towards its field and sometimes away. This leads to classical stellar aberration (discovered by Bradley in the 1700s; Bradley was a genious, IMHO), which leads to a beaming effect, in which the field-of-view (or plate scale) changes with the projection of the velocity vector onto the field-center pointing vector. A measurement of this would only take a day or two of hard work, and would provide a measure of the speed of light in units of the velocity of Kepler in its orbit.
