Transactional Email Sending Through On-Demand Flow without IndividualId

We have a transactional email send use case and the calling application will not know the required SF IndividualId and/or the contact may not exist in SF yet. 

Documentation states requirement to provide IndividualId   

Send Transactional Messages Through On-Demand Flow | Manage Transactional Messages | Marketing Cloud Next | Salesforce Developers 

{ "inputs" : [ {   "EmailAddress" : "XXXXXXXXXXXXXXX@XXXXXXXX",   "IndividualId" : "XXXXXXXXXXXXXXXXXX"   } ] }

As per Nobuyuki Watanabe @marketingcloudtips - 

SFMC Tips #182 : Marketing Cloud Next: On-Demand Flows with REST API | by Nobuyuki Watanabe @marketingcloudtips | Medium

 "Note: Use an 18-digit Salesforce ID for the IndividualId. If you enter an ID that does not correspond to an existing CRM record, an error will occur during flow execution." 

Is there a way to bypass the IndividualId? and/or what alternative options are there?  

Thanks