Just in time for halloween - we have some serious thread necromancy.

How about some Vic's Vapor Rub ..

How about Melodyne's formant tool? Would that do anything? For this 9 year old pre-Melodyne problem, that is. 

Thread back from the dead! Formant tool might work, but it moves all formants with one tool - it's used to scale the size of the entire vocal cavity. What would be cool is if they provided control over each individual formant, so you could control the resonance(s) of just the snuffy nose (or shrill nose, as the case may be).
 
The Breathe-Right strip was an interesting suggestion.
 
(But seriously, in 9 years, the OP could have had rhinoplasty by now. Or some serious vocal coaching.)

To me, "nasal" can mean two things:
1.  The singer sings through his nose.
2.  The singer's nose is blocked (cold, polyps, etc.)
 
It sounds as though we are talking about #2, which tends to make M and N sounds indistinct.
 
One rather radical solution (which may not be appropriate for the material) would be to EQ the voice as though you were going for a telephone voice, but then back-off a little.  This would mean cutting highs and lows significantly and leaving orboosting the middle.  That sounds counter-intuitive, but it might come across as a sound you are going for instead of a problem: that type of EQ makes everyone sound a little nasal (in the #2 sense).  Of course, you probably wouldn't want to get too extreme, and this may not work for the particular song.  This could sound good or horrible.
 
Side note: I find 1176 compression gives a little of that sound if pushed hard.
 
 

For a nasal 'honk', I'd use a multi-band compressor to smash that resonance. Get a picture of the resonance using a very short clip, (I'd personally use SoundForge for this). Then within Sonar I'd use something like the Sonitus compressor to adjust a band to match measured resonant band and its Q, compress it to remove resonance, and maybe reduce it overall in level. Net, I'd use a regular EQ to taste.