So.
Could you go up a milimeter to size 28mm
and then just slip the tile over the live 27mm?
[video=youtube;lYvM8yKDJJU]http://www.youtube.com/watch?v=lYvM8yKDJJU&feature=player_embedded[/video]
Our kits are between £30 and £50
The alternative is to go 3mm bigger and get the 30mm socket.
That is part of the best selling bathroom fitters kit that is £49.99 a kit or £7.15 a drill
Kit contains a 30mm to bore over 27mm pipes (Plus a 40mm, 16mm, 6mmx2, 8mmx2)
The kit will drill hole sizes bigger than you might need (see above)
But most items like this fisher fixing kit are concealed by the actual fitting.
In this case the fisher bolt will be concealed by the sink. So the hole size can be generously larger than the 16mm shown.