I use a very small cone shaped ginding stone that has a well defined point on a rotary tool. Very lightly apply the point to the hole at slow speed and it will debur the drill hole pretty well. Make sure you angle the drill hole in line with the run of the stay. This will limit the sharp edge coming in contact with the stay wire.
The way I did it recently was to get peice of stainless wire - solid - and push it into the hole and rub for a few minutes on the line the strand wire will be - seems to take the rough edge off and I get no chaffing of my shrouds.
Get an old drill of the same size, flaten the drill end, grind a V groove around the drill about an 1/8th back from the end and placing it in the hole carefully rotate the groove around the hole.
The "back" of the hole can also be burnished very easily with a small dentist's probe. Ask your dentist to give you the one he uses on you that causes so much pain.[}:)]