Changing memory size on a single page in CodeIgniter

[eluser]See64[/eluser]
I'm playing around with the image manipulation class, and I'm running into the well known "Allowed memory size of 8388608 bytes exhausted..." error. I was wondering what the best way to temprarily change this value is. I'm only resizing an image when the visitor uploads one that's too big, so setting the maximum to 32MB for *every* page seems overkill.

What is the best way to do this in CodeIgniter for *just* the upload-page?