For charging on cost to work, Mosaic must recognize a cost to pay the provider, which it then uses to bill the client. If the costs are notional, Mosaic doesn't pay the provider, and the client doesn't get charged. This is similar to when Mosaic doesn't include the provision of services in a payment cycle type, so it doesn't see them as payable and won't bill the client.
To make something billable to the client but not payable to the provider using billing on cost:
Use elements that are costed and have real rates (not notional).
Link them to a payment cycle that isn't configured to create an interface file.
You don't need to ever create that payment cycle; linking it means the costs are payable and therefore billable.
There are other ways to make something chargeable, but this method keeps it consistent with how you bill all other homecare services.