how do i prevent blood stains from washing off?

i know this sounds strange, and it's usually the exact opposite here. but my friend is making a costume for her band, she bled at a show once and wants to keep the blood stains on the clothing, but still wants to be able to wash them without losing the stains. i know that when dying fabric vinegar locks in the color better, but i was thinking it might have the opposite effect on blood. any suggestions as to how i can't prevent the blood from washing off when i throw it in the washer?