I'm trying to customize the display of related products using jcarousel, and I can't figure out how to override the block display function without changing the actual module code. Several tutorials as well as the theme developer module keep telling me that I need to copy block-uc_upsell.tpl.php or one of a few other files that don't exist into my theme directory.

I'm pretty sure that I need to override uc_upsell_block_contents in uc_upsell_block.inc, but I have no idea how to do this, and no tutorial I can find about block theming seems to say anything about inc files.

I know this isn't really about this module in particular, but can I get some help?