Nintendo of America, at least, has an item in their FAQ section which states--albeit in a kinder way--that users with a dead pixel on one of their DS screens should "deal with it." (The FAQ does suggest playing games on the DS with the dead pixel for some time to see if it really bothers you.)
However, if the DS is within the warranty period of one year since its purchase, they will still replace or repair the DS in the event that the pixel is a serious bother. Considering that your DS is still in the warranty period, you could have it replaced. There is surely information about doing so on
Nintendo's European site.
Jam it back in, in the dark.