I tried to construct the sentence:
Piki al iu la flankon
Does it make sense? If it does, please translate the sentence 'Nakamura poked Leo in his ribs' or 'Nakamura pokes Leo in his ribs' as an example.
I think you found the best translation already, with the word "piki". The rest is just a question of style.
"Nakamura pikis Leon en lia flanko."
Wells, 2010 gives "piki" as the translation for "poke" and so does CEED. Reta Vortaro has "poke fun at", but not "poke" on its own.
Yesterday in "La Kastelo de vitro" de John Francis I read the nice verb kubutumi, lit. "do something with the ellbow", in the very meaning of "poke someone in the ribs". It is neatly understandable IMHO.