There is actually. Assign a city to produce a shared project until you have contributed the number of hammers for the prize you want, then set the city to produce something else. Let someone else produce the hammers to actually complete it.
That wasn't really the question, but yes you can do that. That is sequencing production, not splitting production (diverting some production per turn to two different build items). In fact you could (if you were a masochistic micromanager) alternate production each turn (worlds fair one turn, workshop the next, back to worlds fair next turn, back to workshop next turn, etc. etc.).