I can hear mild tinnitus in a quiet room when I put down the headphones after about an hour of straight listening.
In an attempt to relieve my ears of fatigue, I went to the drug store and bought myself a box of cheap ear plugs. I got about 50 ear plugs for $8 or so. Before I went to sleep that night, I inserted the ear plugs, which made the ringing more up-front and close. Since tinnitus is as much physical as it is mental, the ringing became louder and louder as I concentrated on it. It's a bit of an endurance test if you let it bug you, but as I got up the next morning, I noticed the ringing was gone.
I can't guarantee everyone else will result in the same experience, but don't take my word for it, it might just not work for you. Also, some of you guys are probably thinking of using IEM's like Shure's to try this out with, I would highly *NOT* recommend using them as ear plugs, I've heard of serious accidents associated with them on these forums. Using certified ear plugs is your best bet.