I have added a few custom columns to my queue through some hacks, and I can confirm that they show up on my export.
I have not modified the class.export.php file.
But I have done the following to my tickets.inc.php file:
However I have an issue where I only get a single row in the export... but this is not related to my code changes as it was happening before I made them.
So hopefully the above helps in someway.