Have you gone to a lab and asked if a phlebotimist can take a sample and give it to you?

I believe those vacuum tubes they use to draw blood have an anticoagulent in them.

Then a laboratory grade rubber stopper and he will have what he wants... Add a silver chain and he can even wear it around his neck.

Google this and get 20,600 more ideas, some of which appear to answer your question directly. "blood vial jewelry"

I would pay heed though, to concerns raised by fetish... remember, just because you heard it on the Internet... doesn't mean common sense and caution needn't apply.