Code

var layout = new AnnealLayout();
layout.KeepGroupLayout = true;
layout.LayoutArea = diagram.Bounds;
layout.SplitGraph = false;

while (NodesIntersect())
	layout.Arrange(diagram);

diagram.ResizeToFitItems(5);

bool NodesIntersect()
{
	for (int i = 0; i < diagram.Nodes.Count - 1; ++i)
	{
		DiagramNode node1 = diagram.Nodes[i];
		if (node1.MasterGroup != null)
			continue;
		for (int j = i + 1; j < diagram.Nodes.Count; ++j)
		{
			DiagramNode node2 = diagram.Nodes[j];
			if (node2.MasterGroup != null)
				continue;

			if (node1.Bounds.IntersectsWith(node2.Bounds))
				return true;
		}
	}

	return false;
}