How to rear vent my Bosch Exxcel Tumble Dryer WTA3204GB/09?

I currently own a Bosch Exxcel Tumble Dryer WTA3204GB/09. It is set up for side venting but I need to change it to rear venting as I am re-siting the dryer. The adaptor for the side vent fits around the outside of the rectangular opening on the dryer. (There is a gap around the opening and the opening has a protruding lip which allow for the adaptor to fit around the outside). The other side of the adaptor is ciruclar which allows for the attachment of the ventilation hose. However, the rear vent on the machine does not have the gap, nor a protruding lip. The rear opening is flush with the back panel. The rear opening is the same size as the side opening. Is there an adaptor available for the rear opening that I can use? Perhaps something that can fit into the opening (not around)? I've called up Bosch and they said the current adaptor I have is the only one available for this model. They did not offer a solution for me. Not very helpful. What can I do to have this tumble dryer vent from the rear?