I have to call domain A.com (which sets the cookies with http) from domain B.com. All I do on domain B.com is (javascript):
var head = document.getElementsByTagName("head")[0];
var script = document.createElement("script");
script.src = "A.com/setCookie?cache=1231213123";
head.appendChild(script);
This sets the cookie on A.com on every browser I've tested, except Safari. Amazingly this works in IE6, even without the P3P headers.
Is there any way to make this work in Safari?