Custom reports apply to multiple websites

When creating a custom report you can choose to what website the report should apply to. You can choose between a specific website or all website. We would like to select multiple websites, but not all.

Our use case:
We created a report that shows some insights on specific custom dimensions. These custom dimensions only apply to 2 out of 6 websites. When selecting “Apply to: All websites” you will get the following error: “The given “Dimensions” at position “1” does not exist.” Which is correct because the custom dimension is not set for all websites. We would like to select both websites in this selector.