I hope I understand your requirement. You are working with an external system and want to be able to pull list of items from the external system. This can be achieved by using qSIListView and it seems that you are able to do that. Once the data is pulled in and displayed in the qSIListView Web Part, you want to be able to create a custom action to be associated with a context menu or toolbar button so when user select an item in the list, the user can click the menu or toolbar button to open up a form and modify/update/edit this selected item. In particular, there is a field in the form that you want to update using a people picker. Is the scenario described correctly, my suggestion is as following:
1. Add a custom action as Context menu item and add a "Go To Url" action to the action item.
2. Specify "Go To Url" action's URL property to the page where you will add a qSIListForm to update the external system item and specify the parameter as HttpRequest query string so you can pass the ID or other key value to this page from qSIListView
3. Create a Web Part page to be the target page of the previous step and add qSIListForm Web Part.
4. Define Catalog property so that the default entity/operation would be to pull out the external system item based on the key or ID passed to the page (as HttpRequest parameter type).
5. For the field where you want to assign a person to the underlying list item, you want to define it as a Choice field and either define the choice items manually, or define an entity/operation/parameters to pull a list of persons, and you have choices of using a dropdown or an item picker, which functions similar to a people picker.
6. Define you update/save actions to be associated with a Save button. You would also need to go back to Catelog property to define an entity/operation/parameter to fullfill this action, which reads the input data and update to the external system.
Now if you goal is to update a SharePoint list item with one field and have the value from a list pulled from the external system, it will be much easier.