I want to set the requested for property on a vac request via vci so that I can control the post install approver. any ideas on how to do this?

I want the user to be able to select the approver from a vcac request. My idea is to have a drop down list of approvers selectable by the user. I would then attach a vci workflow to the building machine stub which would update the requestedFor property This would then allow my to set a post provision approval level based on that field. This issue is I don't know how to pass the requested for field to vci so that I can modify it.