Convert gif to jpeg on the fly using gd?

I have a class that only accepts jpegs and png's but all of my images(we have over 200 of them) are in gif format. Is there a way to convert from gif to jpeg on the fly without outputting the new image to file or the screen or using a system call to run the gif2XXX utilities? I've tried imagejpeg(imagecreatefromgif($image)) but it outputs the image to the html screen as it should. Granted, I could pull some neat output buffering trick but I want to know if you guys think there is an easier way. And if so, point me in the right direction Thanks, Brent