They should just line up a bunch of apples, worked for Newton...
Seems to me that you could measure the absorption lines of a certain element in a star’s spectrograph, via a satellite in constant optical contact with that star, 24 / 7 / 365, then measure the amount of red or blue shift, indicating that star’s direction of movement, either toward or away from the observer. It should be constant, or nearly so.
Then, monitor that star’s spectrum constantly for a long period of time, and check to see if that absorption line moves, either way, up or down the spectrum. That would indicate that a gravity wave had passed between the star and the observer satellite, stretching then contracting the fabric of space-time between............................
Sound okay?..................