Are you using a breadboard or just a board with holes in it? Either way, you can simply bolt the heatsync to it and have it stand straight up, like this
[PoorASCIart]
Code:
[
[]|
| [
-----|---------
[/PoorASCIart]
If that made sense. I can try to find pics.
EDIT... Just read your post... properly... I guess you could drill a hole in the tin and use the bolt hole for what it's intended (a bolt), and simply secure it this way. You may have a problem with the contacts touching though... not sure of exactly how it looks.
Jacob