Michael - definitely no need to have a temp SF object for this. I do this all the time in Skuid.
Your second model should have a condition that uses the value content of “Field from another Model”. Source model will be your first model, and source field can just be Id if both models are built on the same object. Also make sure the Id field is included in both models. Then set the operator to ‘not in’.
This will cause your second model to query any opportunities where the Id is not found in any of the rows within the first model.
