Pete Juliano, N6QW, has written an article on how to do CW on a homebrew SSB rig:
The Answer is Not a Flippant: Carefully!
Author’s note: A friend in VK4 land made an inquiry about CW operation. I find that 99.99% of my operating time is SSB. But others spend a greater time on the air using CW so why not share some info and data that I have stashed on my computer where a SSB rig can be made to work CW. This also open the possibility of filter switching for a more narrow pass band. With Arduino anything may be possible.
More details on Pete Juliano’s (N6QW) blog.