I've taken Spanish before, so I've been able to practice more. Although I had a lot of trouble, to begin with. The trick I used is what I like to call the "Pigeon Call" technique. You make a warbling sound like a pigeon, and this will give you a general idea of how the r-trilling works. I would suggest making that the temporary sound you use in replacing the trilled "r," then after you master that, you can trill your "r's" better. I hope that helps.
Hmm, I do believe the letters are coming, since the volunteer team announced weeks ago that they had requested them to be added to the course, although for the life of me I cannot understand why it takes so very long. If you don't want to install a new keyboard, or keep copy-pasting the letters, I have no other suggestions for you than to wait for the update, unfortunately. :(