Another thing you could try although some will advise against it. If you have a humidifier, get some of that Vick's Vaporub and mixed it in with warm water.
You're right. I would advise against it. I'd be worried that it would leave a film inside the hose, which would be real hard to get clean.
In addition, I've read that you should not use any petroleum products as it could be harmful to the silicon in the mask.