Hi there,
Splitting delivery of email is possible with the Symantec.cloud service but only with the use of the Data Protection for Email product. This product allows you to create policies with an action of 'Route to'. If you have not done so already I suggest you call the Symantec.cloud service desk where a cloud support agent will be happy to assist you. Please call your regional number listed in the link below:
https://support.symantec.com/en_US/cloud/cloud-technical-and-language-support.html