The CorningWare browner works on a simple principle. It is lined with a material that can absorb microwave radiation (just like water does) and therefore become hot. Then when you add your food, the hot surface of the pan browns it. Seems like an effective solution in the situation you describe, where you really want to cook with a hot surface but can't use normal means in the enviroment you are in.
Sunflower lecithin (sorry, best link I could find) is gaining in popularity as an alternative to soy lecithin because it is widely perceived to have a neutral taste and actually has superior emulsifying properties. It's a little on the expensive side, though.
Soy lecithin by itself doesn't taste horrible if you buy it as a food additive (as opposed to a nutritional supplement). It's common to find in a lot of popular frozen pasta-and-sauce dishes, such as Michelina's, which obviously must be microwaveable without the sauce curdling or separating.
Another option is Sodium Stearoyl Lactylate, if you can get hold of it. This one adds a little sweetness which is generally pleasant-tasting, or at least inoffensive. You'll find it used most often as a dough conditioner or in baked goods, but another popular use for it is in commercial sauces, although unfortunately I can't find specific examples right now.
But probably the best emulsifier for what you're trying to do here is xanthan gum. It's also used as a gelling agent, but in small quantities works as just an emulsifier. You can find it, for example, in this Bertolli Creamy Alfredo Pasta Sauce - exactly the sort of thing you're making. It's also used in the Stouffer's Alfredo sauce.
Mix in a little lecithin or xanthan gum as an emulsifier while the sauce is fresh or cooking and it's very unlikely that your sauce will separate, either in the fridge or in the microwave.
As for what you can do to specifically prevent separation while reheating, if you didn't add any emulsifiers in the first place... I really don't think there's anything you can do. If you're a slow enough eater the sauce will eventually separate right in front of you; that's just what happens when you have water and fat in the same sauce. Best to reheat on the stove top in that case, and stir frequently to prevent any further separation.
Best Answer
Frozen hash browns like that are already pretty much cooked. When you bake them, you're really just heating them up and crisping the outside.
If you cook some then save them, they're going to lose a lot of that crispiness no matter what you do. If you eat them cold they'll be, well, cold. If you heat them in the microwave, they'll soften even more. If you still like them, go for it.
Safety-wise, it's fine. You do need to keep them in the fridge, as with pretty much any other leftover food.