Here are some important points to remember:
1. Do not use pedals at first.
2. Choose a registration of one nice flute.
3. Don't worry about the names of the modes, simply say to yourself the number of accidentals.
4. Change the number of accidentals randomly.
5. Change the accidentals every 15 seconds or so to keep it interesting and colorful.
6. Start by a simple flourish in one voice texture in the right hand.
7. Then add a drone in the left hand which would fit the mode you are in currently.
8. This drone can be a single voice at first or an interval of two notes later.
9. After a while move the drone to the pedals played by the soft 16' and 8' stops.
10. As you play, imagine or remember a moment in your life when you saw a beautiful morning with pastures, clear skies, small droplets of dew on the grass, and a little chilly feeling in the shade which becomes warmer as the sun goes up.
Here's my example.
Feel free to post your example online and share the link in the comments here.