I would say that as a general rule he cannot. The special case of trolls is a good point, but the prospetive troll is REBORN and has a new mother; I would still make it extremely difficult. Why would the shaman or the ancestors want some non-family member worshipping them? Why would anyone worship someone who wasn't their ancestor? Perhaps if ancestral spirits can be traced back to Grandfather Mortal then a shared cult is possible. Bear in mind that (assuming you trace both male and female ancestors) after 10 generations you should have 2048 ancestors (ignoring the effects of inbreeding).
Keith Nellist
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