As an alternative, you might consider a PFD safety strobe. NRS carries one at
http://www.nrsweb.com/shop/product.asp?pfid=2924&pdeptid=2120

These are very bright strobes designed to clip onto a life jacket. They USCG approved emergency signaling devices and are waterproof. With a bit of duct tape you could attach them anywhere.

NRS carries several other types of strobes at
http://www.nrsweb.com/shop/product_list.asp?deptid=2120

I have no commection to NRS other than that I have purchased stuff from them in the past and have been very satisfied with both the quality of the gear and their service. These and similar strobes are also available at other retailers that cater to sea kayakers and boaters.
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"Toto, I've a feeling we're not in Kansas any more."
-Dorothy, in The Wizard of Oz