api question

I'm afraid it is not available directly, you'll have to do something rather tricky: use microsoft's windows API to obtain the mouse pixel position in your ModelView, then ModelView::Transform to obtain the XYZ position in model space then use ModelView::GetEyePoint to define a vector going from your eye through the obtained point and finally ModelDoc::RayIntersections+GetRayIntersectionsTopology, quite complex especially in assemblies, to obtain the desired points. Another way is to request apisupport to implement this api, and wait a few years... Maybe you'd rather stick to selections...