This may be of interest to you, a number of years ago an old Manx fellow told me that the "a" was added to Fargher when the name was being recorded in the Parish Register's of the Established Church. due to many of the incumbents being English, and that the Manx tended to roll their "r's", so that the "r" sounded like "ra" and so was written that way.
I hope this is clear and of interest, it may well be wrong!
Take care now
Tony