I must presume that each of the races share some common tradition that goes back far enough that they value it more than any current conflicts. For the purposes of answering the post, I'll presume that there is some common desire for peace/goodwill which can overcome small conflicts.
Tokens.
Let the tokens be something that call upon the cooperation of the races. The dwarves might craft fine amulets, capable of being charmed. The halflings might perform the intricate carvings/artwork. The elves might enchant them with a protection against evil outsiders, or undead spirits. The gnomes might bind those amulets to the earth itself, as they act together to surround the body completely.
Essentially, it boils down to a charm of protection for the afterlife, and the ritual to create that protection calls on the good intentions of each of the races. To gain that kind of friendship, is perhaps more important than the charms themselves. Should any of the races fail to send an appropriate craftsperson to complete the ritual, then the charms are useless.
Visitors of other races might be unwelcome in a foreign city, but they might say something like, "if your kin were ever a true friend of ______, then you would be my friend." Of course, such lines could just as easily be abused by those who haven't the desire to reciprocate such kindness. But, it is there nonetheless.
While few should be so presumptious as to expect such an honor when they die, when one of the races does not show up to an important burial, it might be the kind of insult that can start a war. It's important to think of the possible implications of not sending an ambassador.
Alternatively, each race can completely craft their own charm. Dwarves craft one to repel undead; elves craft a charm to repel demons/devils; halflings craft a charm which symbolizes abundance (of food, cheer, friendship); gnomes craft a charm which protects from the elements of nature and time.