renaissance poisson

For that matter, you could also immerse it in water in the oven; the water will regulate the temperature to a consistent value below 100C regardless. Though I suppose it takes rather a while to get water hot in an oven....

Alternately, if below-the-boiling-point-of-water isn't quite hot enough, some sort of thing like the terra-cotta containers for baking garlic in ought to work to hold heat and even out the temperature a lot.

Or, for the toaster oven, you should be okay if you put an aluminum-foil tent over the pieces; that will remove most of the proximity effects from the heating elements.