In reply to Jack Wallace:
If your worried about it then having an extra person attached with a sling or clove hitched to the belayer will work very much like a ground anchor at an indoor wall.
Or having the extra person holding the back of the belayers harness will help to keep them near the floor, but give them more movement if needed.
Cheyne wears is mostly on a boulder beach, so you might be able to find an appropriate boulder to attach the belayer to.