I have created a circle on the fly, but I failed to create a radius line with text showing the radius in miles. I have created a circle dynamically using the following code:
var circle = new Circle({
center: [31.0928, -17.9318],
geodesic: true,
radius: 2,
radiusUnit: units.MILES
});
For convenience, here is my JS Fiddle: http://jsfiddle.net/scriptstar/rL5nyt9j
All I have to do is add a radius line and text something like the picture below.

I have made few update to your demo and added the line and the text.
See a working demo here: http://jsfiddle.net/12nymwoL/