Changing the z-index (order) of shapes and connections of Telerik RadDiagram

I am using Telerik RadDiagram for building a diagram. The gray lines are over the shapes (requirements, development etc) in my diagram. Is there any way to put them behind the shapes?

// ... getting ready the shape objects ...
for (int i = 0, j = 0; i < monthCount + 1; i++, j = j + 2)
{
// ... getting ready the shape and connection objects...
RadDiagram1.ShapesCollection.Add(shapeForLines[j]);
RadDiagram1.ShapesCollection.Add(shapeForLines[j + 1]);
RadDiagram1.ConnectionsCollection.Add(monthLine[i]);
RadDiagram1.ShapesCollection.Add(labelMonth[i]);
}
for (int i = 0; i < 7; i++)
{
if (i < 6)
{
RadDiagram1.ShapesCollection.Add(shape[i]);
}
if (i < 7)
{
RadDiagram1.ShapesCollection.Add(label[i]);
}
}