Get a bottleneck for a slide guitar. Put some electrical tape over one end, and slide the bottleneck over the mic capsule.
Crown mic user Ernie Garner came up with this clever way to protect the CM-312A headworn mic capsule when it is not in its carrying case. From a hardware store or home improvement store, get a 1/2-inch I.D. 45-degree piece of plastic electrical conduit, also called rigid PVC conduit. Cost is about 68 cents. Slide it over the mic capsule and the boom.