How to add player name to entity's custom name?

How can I place a player's name into the NBT custom name of another entity? I can link a player to an entity via a UUID scoreboard, but I want their linked entity's name to be "[Username]'s Heart." I am aware of the "{"selector":"@p[whatever]"}" strategy, however this does not work for custom names because they require an int, or string, input and selector requires a list tag.