The new tab list packet provides the ability to set a display name upon using the ADD_PLAYER option of the packet. The value however is ignored by the client (looking at the code it appears to have been overlooked as it is decoded, just not used).
Note for people experiencing this: It is still possible to work around this issue by sending a packet with the UPDATE_DISPLAY_NAME option immediately after the ADD_PLAYER one specifying the display names of the players.