if you have not already i would suggest you try "ultimate rotation". it is the only rotation app i have experience with but it has a "force" option that works well. i'm not sure that it will create the ratio you want since it is non-standard. if you have tried it and it does not work or if you do try it and it does not help then i'm not sure what a next move can be. a search brings up a unity routine called AspectRatioEnforcer,
http://wiki.unity3d.com/index.php?title=...ioEnforcer
here are returns from a search on the routine,
https://goo.gl/L5zRaj
of course this means you need to know how to work with unity but if faced with the issue myself and knowing some unity i would learn what i needed to implement it. this of course assumes the routine will do what you want and that you otherwise know how to create an android app because if the routine covers the bases you need it will be running the kiosk as an app to handle the screens display.
http://wiki.unity3d.com/index.php?title=...ioEnforcer
here are returns from a search on the routine,
https://goo.gl/L5zRaj
of course this means you need to know how to work with unity but if faced with the issue myself and knowing some unity i would learn what i needed to implement it. this of course assumes the routine will do what you want and that you otherwise know how to create an android app because if the routine covers the bases you need it will be running the kiosk as an app to handle the screens display.