West Marine sells some fold up beverage holders. You could mount them either on the side or on the top right front panel, if it is very steep. You could also use a wooden wedge to bring it back to 90°. If you make it of teak or mahogany and use some of varnish, it would keep with the look you have. A very nice look indeed!
Just my 2¢ worth. Good luck and take care.
