Sorry Nimble, there's not way. :(

only way to manage the fish/mercury issue is to eat the bigger fish (halibut, tuna, swordfish) only once a week, and if eating more frequently, eat smaller fish and farm-raised fish.

Fish are essential because of the fatty acids. Can't say enough about how important Omega 3 and Omega 5 fatty acids are; I get them via flax seed oil, but fish oils make the EFA's more bio-available.

I've heard of a supplemnt that is called "Pharmeceutical grade fish oil" that has all metals and toxins removed. Generally, fish oil supplements are highly contaminated and I won't take them, but if I find this new product I'll get it for sure.

Hope that helps! :)

Nimble, this is just my idea, but I understand that the mercury is bound up with the protein. Basically it is part of the fish muscle. That is part of what makes it so terrible! In order for it to come out, the muscle would have to disintegrate, and then it wouldn't exactly be edible fish anymore, maybe some kind of mush.
That said, I guess it wouldn't hurt any to give it a Bentonite marinade. Might help.
You might consider going to mercola.com I believe he has found a fish that has been shown to be free of mercury and pesticides, you could order that to eat occasionally and enjoy without worry.

Squeaky

There is a way to "clean" fish of heavy metals. Yes fish (especially the bigger ones - e.g. swordfish, tuna, shark etc) do contain mercury, but it is nothing compared to the mercury that is leeching out of your teeth this very second.

The way is the natural way which several native diets have discovered (e.g. the mediteraneans) which is to cook fish with garlic. Garlic contains thiols (sulphur compounds) which are strongly attracted to mercury and other heavy metals. They will quickly bind to the mercury rendering it harmless, and it can then be escorted out of the body.

I read about this tip in Dr Blaylock's "Nutrition secrets that may save your life" which I thoroughly recommend.

So every time you cook fish, just throw a couple of cloves of garlic in for good measure. I've started doing this regularly, and I must say just from a taste point of view it is great. Also I feel better for it.