Neat idea. To sell it to the "elites" you'd want to try to casually include stuff known mostly just to them, but not wild rumours. Doubt they'd care.

The problem is there's a simple solution for the elites... Assemble all the elites who want the immortality but think the others have it, then each openly gives 100ml of their blood, openly mix all the blood together, openly pour out equal shares and then each will drink a 100ml of mixed blood. Find a way to add some poison and maybe something good could come of it.