Yes, you can buy an internal inner assembly – just calculate the cost of the keyboard you want and then subtract $110, the cost of the case. Then you can order it using the store item $1 increments.
Would it fit and work well, I can’t guarantee that; it would need to be done at your own risk.
What about converting the original board using this PDF guide:
https://geekhack.org/index.php?topic=48950.msg2848376#msg2848376