Got any easy way to get A/D conversion filtered?

Problem: I got filtered, noiseless 2.5V in ANx and ADCIN gives result which keeps jumping randomly betveen 496..527, which is way too much for me..

I'm affraid I got no time in my code to make multible measurements to average the value.. Does anyone got fast way (for 18F458@20MHz) to make filtered A/D conversion, using other than (slow) ADCIN-command?

Thnx adv!
Marko