A big thing to bear in mind is that most people can't/don't hear distortion the way us sound geeks do. The only time they really do notice is when it draws attention to itself. That is, most people won't notice unless it's really pervasive (present throughout the entire spectrum) or particularly sharp (in the upper end of the spectrum). So your problem isn't getting rid of all of the distortion, just the annoying bits.
If you don't have access to any noise reduction software (expensive) I find a great trick is to take a filter that can do a 24dB/8va cut (EQ3 1-band in PT), set it to low pass and roll it down as far as you can go. Chances are you'll get down to about 7-7.5kHz before stuff starts to get too dull to be conscionable. If you need to go further, try lightening up the curve to 18 or 12dB/8va.
Alternatively, if your distortion is more localized, take a band in a paragraphic EQ and set the Q to about 5-7 and sweep through the spectrum. Generally speaking, most of the annoying stuff in distortion occurs up above 2.5-3kHz. For me it's usually somewhere around 8-10k. When you find it, just dip it out. You'd be amazed how much you can push before things start sounding really dull/bad.
If this isn't a recurring problem I would second the idea of d/l-ing a demo of the iZotope stuff. It really is fantastic.