Try making a little more than half - if you use 3 eggs, you can multiply all the other quantities by 0.6 to make a smaller (3/5) version.

How to do 3/5 of a cup for measuring flour or sugar:

get a straight sided cup and a strip of clean card (eg. from the top of a cereal packet). Put the strip in the mug, mark the height of rim, then measure the distance (easiest to work in mm for this). Multiply by 0.6, mark the resulting length on the card strip and use it as a dipstick.

OK, so a few alternatives I have used in the past:

1. Beat (assuming it needs beating) three eggs together and don't use the last bit.
2. Use 2 large eggs and a third egg yolk, though this might slightly alter the character of what you're making.
3. Use 3 smaller eggs than the recommendation (i.e.small instead of large eggs).
4. Scale everything up slightly to make 3/5 recipe instead of 1/2.

Hope that helps.

If it is a recipe where quantities are important and I am halving a recipe for the first time I normally put the eggs in a bowl and add all but the last bit and then add the extra at the end if I need it.

If it was a quiche type recipe I would probably just add the extra half.

I usually would beat all five eggs together in a one cup measuring cup. Then dump out half into my recipe. Save the other half for scrambling in the morning.

I've found most recipes have room for variations, so either use 3 smaller eggs, or just use 3 eggs. That will be close enough for a huge number of recipes. Don't make it so complicated.