That, to me, sounds like what you use drillPick() for; iterate over the result till you get a circle.
So, a lot of this kinda stuff comes down to how you’ve put your application together, and how you work with entities and the mouse. To me, it sounds like you’re making a draw-line-tool; click the map, a line now follow around from the initial point to the cursor, and a second click on something is the line done.
But the question then is, with your second click, do you want to draw a line from the initial point to the second point you clicked (exactly), or to the circle (either at the edge, or the center) more abstractly?
If the latter, here’s what I would do. When you create an entity it’s often helpful to add a property to it that you can recognise, and then look for this property when you do a drillPick(). For example;
// other stuff here, and then ...
name: 'My red circle',
// and the rest
In drillPick() you get back entities, just do a find on any entity that has that property. If you find it, use the center point (or center point plus the diameter offset to the edge) directly instead of trying to trick pickPosition() into things it can’t do.