Morning Torben,
I have seen people trying to develop something similar to this idea.
Its not easy, it can be done using accelerometers to calculate the offset distance from the Datum.
We did a 'heave compensation' system for Inshore Survey vessels, it does work, but its not cheap and the accuracy we had was about +/-0.1mtr at best.
A stationary, scanning laser leveller [very narrow beam] is positioned at a known height ref point, from which the remote receivers measure their offset, to do what GB is trying.