Yes it is.Hey guys how can I change the aspect ratio to fit into handheld borders? The presets don't fit and I found somewhere that you have to put the aspect ratio to custom and then e.g 4x4 for gameboy but custom ist no option in retroarch wii u
You need to go to Settings -> Video and then change the Aspect Ratio until you hit "Custom".
Once in custom, you can make use of the X and Y offsets right below the Aspect Ratio option.
Change them to your liking, and once you save simply back off and go back to the game, the new aspect ratio should be applied.