I found the Ioniq 5s cup holder to be annoying as it did not fit smaller items, bottles or cans without wobbling due to it not haveing any supports in the middle.

I have designed this simple insert that has a perfect fit due to being built around a 3D scan. It features a 3D printed spring that gets slid inside the main body then has 2 plates glued to the either end. The new insert allows the plates to press againt smaller items preventing them from rattaling.

How will the spring works will depend on your exact filament so you may need to try it with some different ones to find the perfect stiffness and flexibilty.

It should be a tight enough fit over the existing rubber piece in the holder.