QEMU does something similar:
https://github.com/qemu/qemu/blob/master/LICENSE
I think you could phrase that better. Maybe something like “This projects builds on GPLv2-licensed code, so the project is GPLv2-licensed. If you want to use our additions in isolation, you can choose to use them as either GPLv2 or MIT licensed”?
I think you could phrase that better. Maybe something like “This projects builds on GPLv2-licensed code, so the project is GPLv2-licensed. If you want to use our additions in isolation, you can choose to use them as either GPLv2 or MIT licensed”?