How do I distinguish between left and right keys (CTRL and ALT)?

I started making use of Win32's raw input features to detect all keys on the keyboard. So far, everything is working great! I can distinguish between numbers on the top row and numbers in the keypad on the right. I can even detect between the left and right shift keys. However, the control and alt keys do not return unique scan codes. The control key returns 29, and the alt key returns 56.

The popular method for checking key states on these keys is GetAsyncKeyState. I have tested that function using VK_LCONTROL and VK_RCONTROL, and it works, but that only helps me for capturing key down events. I would really like to be able to capture key up events as well. It is obvious that the API is somehow aware of which key is being pressed; how do I get ahold of that information?

I am currently extracting the scan code from the RAWKEYBOARD structure's MakeCode field. That gives me information about every key (and its left/right alignment) except CTRL and ALT. How would I go about capturing the key up events (and knowing whether it is left/right)? Is it possible using just the RAWKEYBOARD structure? Or do I have to concoct some kind of workaround?