Yeah... unfortunately not going to happen. During the design phase of these accordions, Roland made the choice to implement the stereo image according to their specifications... and in their eyes, there is no stereo image where one gets 100% separation from left and right sides, so that means that even with the sound settings set to 100% left or right, you will always hear some signal on the opposite side.
Me, in my past setups with other MIDI instruments and accordions, I very often used 100% sound panning for certain sounds for best effect because I had the option of panning full left, right or anywhere in between... unfortunately though the V-accordion has the ability to have 2 channels, it does not offer the option of full panning control. In essence, we are stuck using what Roland decided for us is best.
By the way, you are far from the first person to ask about this. I've heard it several times before and in my own research tried different settings a few times... no luck and confirmation from Roland themselves supported this fact.
There are some ways one can work around it in multitrack recordings (record a sound/instrument to a single track and via software pan it full left or right), but in setting it up for a live performance... just impossible to do. The good news about that is that normally in live performances, one doesn't often need a 100% full left/right pan for best effect.
