On paper, the "trivial" approach would be to pull Dimension twice - once as Sales_Forecast_Dimension, and once as Case_Volumes_Dimension. This would break the loop, but it does mean all of your fields will be present twice and you will have to pull the correct ones based on context.
Another potential approach is to concatenate Case_Volumes into Sales_Forecast. I'm not sure what the data represents, so I have no idea if this is feasible for you, but it would break the loop.