If this option is not feasible or you would prefer to create privacy in a more minimalist and less costly way there are plenty of alternatives. Firstly, why not consider changing the glass pane to a frosted alternative which will still allow the light to enter the room whilst also blocking the gaze of prying eyes. This option does not necessarily have to mean buying and installing a new pane as there are plenty of spray on products which will give the effect for half the cost and effort.
Furthermore, why not consider using templates to create a frosted pattern to complement your overall design scheme. Consider contemporary mosaic style squares, a floral pattern to match your stained glass windows or a retro circle pattern to accentuate the curvature of the window itself. Because of the subtly of the colours used this bit of pattern will be somewhat sophisticated and also complement your room should you change your colour scheme.
For a more striking option why not get creative and create your own stained glass window using one of the huge range of stained glass kits available. Before starting on the window itself make a trip to your local glazing company and grab an old pane of glass to practice on. Furthermore, be sure to use a template for your design and temporarily stick this on to the other side of your window to ensure an accurate and neat finish.
With regards to accessories; it is generally advised to leave the window bay empty as not only is the shape of the space difficult to rest things on accessories will also detract from the attention on the window its self. Instead look at the wall as a whole. Consider using striped wallpaper to again accentuate the porthole or create a collage of interesting frames, wall art and mirrors to create a novel framed viewpoint with your window. Whatever your choices do not try and disguise or hide the porthole, instead highlight and embrace this unique and charming feature.