Yes, you can store any data in customData.

You have many ways to do this:
1. Make the second marker in the same location that will contain the circle image, and scale along with the map.
http://infinity-code.com/atlas/online-m … ample.html
2. Draw a circle using the polygon.
http://infinity-code.com/doxygen/online … gPoly.html
3. Draw a circle using UI, and show it over the map.

is there a possibility to show a specified radius around a 2d marker?
I've seen that on one of the pictures in the atlas of examples:
http://infinity-code.com/atlas/online-m … ample.html

The radius could be stored in marker.customData, right?

Thank you in advance