How can I select "Start a Task Process" participants from a list. (Office 365)

I want to be able to select a list of approvers and assign that collection or variable as participants in a "Start Task Process" action.

Imagine that you have a list that contains two columns: a location and an approver.  For example:

Location:      Approver:

Job Site A   John Doe

Job Site A   Jane Doe

Job Site B   Fred Smith

Job Site B   Alex Rogers

My workflow will select all the approvers for a given location, say "Job Site A" and attempt to make them participants in the task process. I can get the list of approvers just fine.  I just can't seem to get them into a format or variable that works as a participant in the "Start a Task Process" action.  One approver works just fine, but not multiples.

I appreciate any advice you guys can give.

Chris