Correct way to fill in a thru hull hole

[aldo]

I would go for the feathering- check out this site, and the fiberglass repair manual.
I believe it describes the process pretty well.
http://www.westsystem.com/ss/use-guides/

[FishStretcher]

That doesn't seem practical for a thru-hull in a laminate that is 3/4-1" thick. That would be a 18"-24" diameter patch for a thru hull at 12:1 aspect ratio!