I also use the 22 note Indian Carnatic scale and have adapted a keyboard thus:
Changing the colour of the black notes helps avoid confusing this keyboard set up with the normal 12 note keyboard. Having 2 colours for these 2 groups of notes helps distinguish between them. Placing the C or DO in the middle of the red group makes the lay out quite symmetrical. Finding one's way among the 6 green notes is of course not easy but it helps to bear in mind that FA and SOL are placed symmetrically in this green group.