Hi Markus !
Appreciate that man
You can donate through the "buy me a beer" button in the main menu of the game (bottom right). Will take you to my paypal donation page :)
Don't think you'll be able to get the extra tracks unfortunately :(
To allow the tracks to appear in the game I do a check on the steam items of the player and I check if he purchased the DLC using steam's API. I can't do it here.
cheers and have fun !
val