to coin a phrase: just do it. this is possible through the api and, apparently, not the ui.
var textGraphic = new CIMTextGraphic() {
Text = "Callout Text",
Placement = Anchor.CenterPoint,
Symbol = textSymbol.MakeSymbolReference(),
Shape = MapView.Active.Extent.Center,
//Leaders is an array of CIMLeader - add a Leader point to show
//the leader, remove Leaders to hide the leader.
Leaders = new CIMLeader[] {
new CIMLeaderPoint(){
Point = MapPointBuilderEx.CreateMapPoint(
MapView.Active.Extent.Center.X - 5000,
MapView.Active.Extent.Center.Y - 1500)
},
new CIMLeaderPoint(){
Point = MapPointBuilderEx.CreateMapPoint(
MapView.Active.Extent.Center.X - 3500,
MapView.Active.Extent.Center.Y - 2500)
},
new CIMLeaderPoint(){
Point = MapPointBuilderEx.CreateMapPoint(
MapView.Active.Extent.Center.X - 500,
MapView.Active.Extent.Center.Y - 5000)
}
}
};