Instant OnTheSpot Arches
These are designed to provide some arch support in footwear in which foot orthotics and other types of arch support when there is just not enough room in the footwear, such as ballet flats which is a common question. They are silicone gel arch pad that is self adhesive, so can be placed in the shoe with limited room.
You can buy the Instant Arches here in Australia or here.