Have you considered putting the ingredients in before the water is too hot to burn you? This is as opposed to putting it in cold, instead wait for the water to warm up but not boiling yet, and then put in ingredients.
You would need to get the timing right but a minute or two shouldn't affect how the food cooks; alternatively, you could adjust your cooking times. This mild inconvenience seems worth it to not have to get burned by scalding splashes.
Another possibility is to try to find a lid in which the center of the lid comes out so only a small hole opens up in the center instead of taking off the whole lid. I don't know if they make that, but it might help your issue if you can find one. I googled but no luck.
However, here is an alternative idea to the center hole idea. You can get a large plastic lid of the right size that is strong enough not to melt. For example a bucket lid from a paint pail you can pick up at the hardware store for $1. When it comes time to add the ingredients, now remove the glass lid temporarily and place the plastic lid with a small hole cut out. Now add your ingredients. After adding the ingredients, now put the glass lid back on.
Effectively, this is a splash guard. Here is a picture:
Additionally, some paint pail lids already have a hole which contains its own lid.
If you want to get really fancy you can make a cut out of one of those plastic lids to fit the lid of a food processor which has a large mouth, and that would be a very good splash guard. I will photoshop a picture so hold on...
ok here you go:
Update: I just came back here because I realized the simplest solution seems to be overlooked. Just wear gloves (maybe those yellow rubber ones?) and long sleeves! Granted, this might not be convenient, especially in a hot kitchen. However, if you really hate getting scalded by splashing water then that is another possible solution to your problem.