I had problems when i stopped playing the organ and started playing the piano (it was impossible to to do an organ performance exam at my college). There is so much expression in the piano, your technique has to be precise to achieve the subtle sounds. With the organ, there is no dynamic expression so its more about playing lightly and with precision.
You have to create a mind set for each instrument. Think that you are playing 2 compleatly different instruments, they may both have keyboards, but they are nothing alike.
I'm not very good at playing 2 instruments, so i was glad that I stopped playing the organ so I could focus on my piano technique.
I don't think I helped you, but I don't think there is any easy answer