I think the right thing to do is to switch to libjpeg-turbo http://libjpeg-turbo.virtualgl.org/
, and compile that with JPEG_LIB_VERSION 62. It's noticeably faster than the bog standard libjpeg (even without the fancy x86/sse/mmx ASM), and 100% compatible (creates bit for bit identical output compared to the old, standard libjpeg in all my tests). I'm using it on IRIX since last October without any negative effects. I seem to have neglected to make a nekoware package, I'll try to rectify that soon (when version 1.2 is released).
There are some programs that require the newer 8.x API, but so far the only one I've encountered is ioquake3, and that brings its own libjpeg source and can be linked statically against that.