If OOTB UI Action -> 'Create new work' is completely ruled out, answer to this post lists a plenty of activities - 

https://pdn.pega.com/community/product-support/question/create-work-activity-launch-flow-work-object

You can use pxCreateTopCase activity.

Thanks,

Kiran.

Hello,

You can have a look into Work-.pzCreateCase (This API is exposed in the palette in process modeler to create a top level/ sub cases within a flow.)

Regards

Mahesh