For such a request assigning a dependency to products is a suitable method. For example, as per the IT Shop Administration guide:
You can define dependencies for products. For example, when a printer is requested, a flat-rate installation charge has to be requested at the same time, and toner may be requested optionally. You can also specify if two products should never be requested simultaneously.
Dependencies between requestable products are created using service items.
When a product is requested, it is tested for dependencies and in this case, dependent products are added to the request.
Please refer to the IT Administration guide here: Specifying product dependencies
This means that you can enforce the requirement for one product when another is requested, and notify the user to such.