Restricting Connections about draw2d

[InannaInai]

I'll answer my own question as I've found the solution:

You have to create your own:
var DragConnectionCreatePolicy = draw2d.policy.connection.DragConnectionCreatePolicy.extend({})

and then edit the
onMouseUp: function(canvas, x, y, shiftKey, ctrlKey)

There you can add an if-statement and change the code:

if(this.currentDropTarget instanceof draw2d.Port){
                    var request = new draw2d.command.CommandType(draw2d.command.CommandType.CONNECT);
                    request.source = this.currentDropTarget;
                    request.target = this.mouseDraggingElement;
                    var command = this.mouseDraggingElement.createCommand(request);

                    if(command!==null){
                        command.setConnection(this.createConnection());
                        canvas.getCommandStack().execute(command);
                        this.currentDropTarget.onCatch(this.mouseDraggingElement, x, y, shiftKey, ctrlKey);
                    }
                }

to -->

if((this.mouseDownElement.parent instanceof customButton1&& this.currentDropTarget.parent instanceof customButton1)
                	|| 	(this.mouseDownElement.parent instanceof customButton2&& this.currentDropTarget.parent instanceof customButton1)
                	|| 	(this.mouseDownElement.parent instanceof customButton1&& this.currentDropTarget.parent instanceof customButton2)
                	|| 	(this.mouseDownElement.parent instanceof customButton3&& this.currentDropTarget.parent instanceof customButton2)
                	|| 	(this.mouseDownElement.parent instanceof customButton3&& this.currentDropTarget.parent instanceof customButton1)){
                if(this.currentDropTarget instanceof draw2d.Port){
                    var request = new draw2d.command.CommandType(draw2d.command.CommandType.CONNECT);
                    request.source = this.currentDropTarget;
                    request.target = this.mouseDraggingElement;
                    var command = this.mouseDraggingElement.createCommand(request);

                    if(command!==null){
                        command.setConnection(this.createConnection());
                        canvas.getCommandStack().execute(command);
                        this.currentDropTarget.onCatch(this.mouseDraggingElement, x, y, shiftKey, ctrlKey);
                    }
                }
                }

The customButton1 in this case are the custom created figures (rectsm diamonds,...).

Hopefully that helps someone else