Velcro
Let me know your address and I will put some more in the post.
I have had my screen on the bike for about 12k miles and never had it come loose. It is important to thoroughly clean the area and degrease with brake cleaner before sticking it though. What I do find is that the velcro will sometimes peel off a bit as you remove the screen from the bike. The solution to that is not to remove the screen. The advantage to the velcro over drilling is that you are not making any permanent changes.
On the other hand if you used a couple of longer bolts at the top with something to act as a spacer, a cm or 2 of pipe for example, and a single short bolt at the bottom you could adjust the angle of the screen. I have thought about doing this a few times but never got round to it. I was trying to think of a way of testing it out without actually drilling the headlight shroud.
Iain