This builds on the codeshare Stephen Bell provided for using a custom field with a select. This uses a multi-select and reads back in multiple values and resets them when the contentlet is opened.
/* When page is loaded, copy the hidden field value to the dropdown, initialValues is an array after split */
var initialValues =
$("#curriculumAssociation").val().split(',');
var iLength = initialValues.length;
for(var i = 0; i<iLength; i++){
$("#curriculumAssociation_field select
option").each(function(index){
if($(this).val() == initialValues[i]){
$(this).val(initialValues[i]).attr('selected',
'selected');
}
});