If you want to add extra moisture to your cakes, then you can do so by creating a stock/simple syrup. Here is a recipe and guide on how to make stock syrup for your pre-baked cakes.
To make the stock syrup, you will need the following:
Ingredients:
100 grams or 3.5 oz Granulated or Caster Sugar
150 ml or ¼ pint of water.
Method/Guide:
Put the sugar and the water into a pan and bring to the boil.
Simmer for approx 2-3 minutes until all the sugar has dissolved.
Once all the sugar has dissolved, turn off the hob and leave to cool.
Once sufficiently cooled, this can be lightly brushed or added to the cakes, which will give them extra moisture and flavour.
You can add it to your cakes when they are hot straight from the oven or after...