There are 3 BLAKENEY's at Brian Lawsons site Burial Index (www.lawsons.ca and click on burial index) the earliest being Robert being buried in 1778 at Maughold.

You will find also that the same Robert Blakeney left a will (Go to the will index at the above site)

At http://www.isle-of-man.com/manxnotebook/manxnb/v05p031.htm
there are a couple of interesting pieces written to Mr W Blakeney in Jan & July 1777 by Rev Philip Moore which could put a light on a connection with Ireland....... (and America perhaps!!) You will have to scroll down to find them

Also there is a Rev Blakeney listed as a resident at St Judes, Andreas in Browns Directory in 1894

And there is a Rev William Purden Blakeney at Stephen's, Sulby listed in Porter's Directory 1889 (possibly the same person as above)

Good luck with your research
Elizabeth