The solution is very simple really.  You can for example write the following:
protected override void CreateChildControls()
{
ImageButton someImageButton=new ImageButton();
someImageButton.Click += new ImageClickEventHandler(ImageButton_Click);
this.Controls.Add(someImageButton);
}

protected void ImageButton_Click(object sender, ImageClickEventArgs e)
{
do something..;
}

within your custom control.  You only want to bubble events when you want to
expose your event in the containing page.