Ok, I;m an idiot. It works the way I was asking, you just have to dereference your custom data off the options object of the jcarousel in the callback.
Thusly, for posterity: // Init jcarousel jQuery('#mycarousel').jcarousel({ itemLoadCallback: {onBeforeAnimation: mycarousel_itemLoadCallback} arbitraryData: "Custom data for everbody!" }); // callback function mycarousel_itemLoadCallback(carousel, state) { alert("Here's our data: " + carousel.options.arbitraryData); }