Catalysis of the reaction: 2,4',7-trihydroxyisoflavanone + S-adenosyl-L-methionine = H+ + 2,7-dihydroxy-4'-methoxyisoflavanone + S-adenosyl-L-homocysteine.
2,7,4'-trihydroxyisoflavanone-4'-O-methyltransferase activity