[Modeler] Select participant from a dropdown instead input with its name

Could someone advise how I can extend or where I have to change the logic in the Modeler in order to add a dropdown with a list with all participants which in general will be loaded from a DB instead of writing the name of the participant as an input.

Thank you in advance.

Let me rephrase my question. Is it possible to implement a custom Taskbox as Dropbox?