I have not had this problem since we live in a fairly dry part of the country. FWIW the chrome gauge trim ring is crimped around the front of the gauge. It would be fiddely to get the ring off, and once removed it would be near impossible to get it back looking right. They are not made to be user serviceable.
The moist air gets in through the gauge light socket from the back side of the gauge over time, especially if you live in a moist climate, and/or the bike sits in the rain a lot.
I like the suggestion of drilling a small hole in the bottom of the gauge case, as was suggested in the 2009 thread. This would at least allow the moisture to equalize, and should prevent a buildup.
If the damage is already done however, I think you are hooped.
Rod