custom date for a post

I want to break the date mechanism in Wordpress. I need to have dates set in the 30 century, controlled through the regular post, but only for one category.

To give an example I'd like a post dated 21st of August, 2999, but published on the 10th of December 2014.

A search has not turned up anything that meets my needs. I'm using custom fields to record the date, but I don't know of a way of making it replace the blog's date for the chosen category. I'd rather not modify the loop or any code, but does anyone have some suggestions how I can make this happen?

Cheers, Jamie