Hi,
It's possible, but not with a tag. It will require some coding.
First, some coding to skip the custom field display in show_block_custom_item.php and second a copy of the code in show_block_cusotm_item.php in the product / option.php view but instead of skipping that custom field, you would skip the other ones (if any). And you need to do that in the foreach on the options before/after the option you want.
If you're a PHP developer and with these indications, that should be totally possible. Otherwise, you'll have to get a developer to work on that for you.
