Right, here is how I did it:
use a david's razor plane with the blade depth set to about 0.5 mm:
Get a length of suitable wood, I used cedar, at a thickness similar to the depth of the mast hoop, run the plane carefully and steadily along the full length of the wood so you get one long continuous strip of thin wood.
Then, find a piece of dowel or plastic tube the diameter of which is suitable for the inside diameter of the hoop, wrap the strip of wood around the dowel, touching the wood with a spot of superglue every quarter turn or so, continue wrapping until you have slightly more thickness than you require, remove from dowel and finish to size by sanding.
Its fiddly and slow, but it works and the end results look ok.
Good luck,
Ian