update:
I managed to kill the numbers in the caption with
$('.caption').text($('.caption').text().substring(2));
before
return false;
in mycarousel_initCallback function
And putting just a space as the caption rather than leaving it blank makes it stop saying "undefined". However, when the mouse pointer is over a thumbnail, it still shows the number (with a space after it). Is there maybe a way to just turn off all the hover pop-up text stuff on all the images on a page?