Here's my current implementation:
$.liveClickHold = function(selector, fn) {
$(selector).live("mousedown", function(evt) {
var $this = $(this).data("mousedown", true);
setTimeout(function() {
if ($this.data("mousedown") === true) {
fn(evt);
}
}, 500);
});
$(selector).live("mouseup", function(evt) {
$(this).data("mousedown", false);
});
}