A cure for pianists trying to play the organ would depend on their goals. Some of them might want to learn to play hymns in church while others - original organ compositions. There are also pianists who would love to learn to improvise on the organ as well. Of course, there is a considerable overlap in people dreams - some people who would want to learn hymn playing would love to play organ music as well. Would-be improvisers might also love to learn to play original organ compositions of classical organ masters.
Here's a cure for pianists who want to learn to master hymn playing:
Take your favorite hymnal and begin learning to play the hymns with pedals. It's best if you practice parts separately first, especially the pedal line. When you can fluently play the pedal line, play two and three part combinations before attempting to play all parts together in a slow tempo.
For pianists who want to learn to play original organ music:
Find easy but quality collections of organ music and learn a few pieces that you like or that fits best the liturgical season of the church year. Make sure you also learn very systematically step by step in a slow tempo. Try to avoid the temptation to play pieces from the beginning to the end without correcting mistakes and all parts together right away. In most cases, you would still have to go back and learn the pieces the right way and develop correct organ practice habits. Learning the pieces correctly in the first place will save you from a lot of frustration in the future.
For pianists whose goal is to learn to improvise on the organ for the liturgy:
Start anywhere. Literally. Just choose a theme (a hymn or your own melody), a mood which would work for a specific place within the liturgy, meter, mode, key, texture, and registration and improvise something interesting. Nobody will tell you what to do or how to do it or that you made a mistake. It's your improvisation. The only thing that matters is that you set your goal to be this: to keep the listener transfixed with your playing and that it would fit the liturgy of today.
It's important to understand the differences from the piano and organ and learn new skill sets that any organist need to be successful. Regardless of your goals in organ playing, you can use the existing hymns, organ compositions or your own improvisations to acquire organ playing skills which you can later use in church service playing.