Interesting. This seems to work for Mac users:
{
"cmd": "/Applications/Safari.app/Contents/MacOS/Safari", "$file"]
}
Except it opens the Sublime console and displayed this 3 times:
2012-02-09 16:34:06.860 Safari[64689:707] CFPropertyListCreateFromXMLData(): Old-style plist parser: missing semicolon in dictionary.
Edit: the messages only happend the first time, when Safari launched. Can you prevent the console from opening on a build, though?