Hi Ross,
The Lawsons section of the IOMFHS site has a wills section, with a entire page devoted to Cowin. Very few have been transcribed and uploaded, and those that have are no use in proving who Philip was, or the Mauritius family. There is one for Patrick (1827, Braddan), Alice (1832, Lonan). My distant cousin in Australia was once a member of the FHS, and she sent me some correspondence from a member/researcher, but wills were never mentioned. She was sent a transcript (typed) of a will of Joseph (died 1888), but he turned out to be from another family. I had a look at the site, and it seems nothing new has been added since May of last year.
Best wishes,
Stephen