How can I address watery eggs in a microwaved breakfast sandwich?

I see two possible problems with what you've described --

1. If you don't freeze the egg quickly enough, you're more likely to have larger ice crystals form, resulting in a puddle of water no matter how you defrost it. You should be able to test for this case by just putting the frozen egg in a covered bowl and let it come to room temperature. If this gives you a lot of water, you can freeze the eggs on a sheet pan lined with waxed paper or parchment, then assemble the sandwiches to freeze.

2. Overheating eggs will cause the proteins to tighten resulting in puddles of moisture. (this is mainly a problem with scrambled eggs or egg casseroles). The solution to this is to heat it as little as possible.

As for the bread soaking through -- you can also look for alternatives. Bagels and crusty rolls hold up much better to moisture, but bagels in particular can end up really chewy after microwaving. A thicker roll would also have more crumb to absorb moisture.

You can also try spreading something on the bread to prevent the moisture from soaking it (although, it can make for messier eating if the sandwich is dripping). For egg sandwiches, I like hot pepper jellies.

Udated: I was able to sit and talk with my girlfriend about these, acutaly we were eating them as we talked.

Ok this theoretical but here goes.

Rice paper, that's right, Vietnamese rice paper. In Vietnam there is a food, Nam Ninh Hoa, It is fresh lettuce, pork sausage, julienne'd carrots and cucumbers, a bunch of different green, a yellow veg i did get the name of and a piece of rice paper that has been folded and fried. you sit at the table and build these and eat em one after the other. You take a piece of rice paper, the paper regular rice paper that has been place it the fridge and that does something to it, slightly pliable. firm but not brittle. put the other ingredients in it wrap it up, dip in a sauce and eat.

For clarity: there is one piece of fried rice paper that is included with the other ingredients that are wrapped up in the non fried rice paper.

What is relevant is to the OP's question is rice paper. Your wife could just cut them to the size of your sandwich thins and then wrap the egg whites in them. kind of like make an egg white sandwich with the rice paper in place of the bread and then put that into the sandwich and freeze. just eggsperiment with the rice paper. you may have to slightly moisten it, spritz it with water?

all of this is to say my answer to the OP is Rice Paper. try it.

When you microwave the sandwich the moisture from the eggs will be absorbed by the rice paper. presto magico. non runny sandwich.

Well, Jimmy Dean uses an egg patty consisting out of whole eggs, modified corn starch and xanthan gum. The modified corn starch helps absorbing water without heat and the xanthan gum keeps everything together in a rubbery state.

Otherwise, I've never heard of frozen cooked egg whites ever being used in a commercial kitchen, only uncooked egg white.

It might help to freeze the egg patty separately from the rest of the sandwich.

This might give you a chance to brush off any ice crystals that form, meaning less water to try and deal with inside the sandwich.

You could either assemble the sandwich when you make it in the morning (with the bonus of being able to heat the elements separately, and possibly discard more water that way), or else after the eggs are frozen, brush off any ice crystals, assemble the sandwich around the frozen egg and put in the freezer again to make your frozen convenience sandwich.

Usually I see more ice crystals when something's been in the freezer longer, one reason why making the sandwiches on a delay might help more (maybe make the egg one one week in advance, assemble the whole sandwiches to freeze with last week's frozen egg?) - but it does work that removing the crystals, brushing the ice off, does dry out the item a bit more.

Also, this might help the egg freeze more quickly - as per Joe's answer - so the trapped water freezes more quickly, does less damage to the egg, and stays in the egg instead of dripping out. The smaller thermal mass means it should cool and freeze a lot quicker than a whole sandwich, where the bread in particular may insulate it for a longer freezing time.

And it might make it easier, working with a sturdy and already frozen egg patty, to dust the egg in cornstarch or wrap it in rice paper or something, if you want another layer to absorb moisture with.