Take your friend down into Central Park, and get on one knee. He will crap his pants, specially if he ain't as homo as me. If you went to the effort of getting cuff links just for the box as well keep wondering around the park after freaking out your friend and just propose to anybody sitting on a bench.
Let me know your friends reaction though, and do it when people are around as well so it makes it even more awkward for him!
Have a good time man