Check out these pants: https://www.facebook.com/chickfly/
https://www.facebook.com/EZPeePants/
Also ... is it even possible to pee without exposing your vulva? It's not needed to expose your butt though
Have you ever used a urinal before? Can you pee into one standing up using the v-finger method, which involves spreading the labia so they do not block the stream, and pulling up so that the pee goes forwards?