This is very confusing to me:
But now my client wants to have additional options that are universal to all clients. He does not want to add them to each rate card, understandable.
Specifically "...universal to all clients." and "...does not want to add them to each rate card..."
So I have no idea which one you want. I would think that universal to all clients mean they show up on all clients 'rate card'.
Universal rate card?
user28271, I do this for a client of mine that needs to show photos for each of a client's locations and also photos that are common to everyone in the whole company.
All companies, clients or vendors, corporate or constituent (subsidiary), are in the same table. Companies are categorized in those ways. A constituent client has a parent key that is their corporate parent ID. [UUIDs are REQUIRED to make this work.]
Photos (also all in the same table) are added in a portal in the company layout, and each has a parent key that is their parent entity, be it subsidiary or corporate.
Elsewhere, when I need to show both sets of photos, I simply have a portal that uses a global for the parent key of the relationship. I then (on record load) insert BOTH the subsidiary key AND the parent key AS A LIST into the global. That will show both sets of photos in the portal.
In addition, a field in photos is set when created that grabs the client type (Corporate or Local). That field is then displayed in the portal (that shows both sets) that indicates which ones are local and which ones are corporate. (As a space-saver and to look cool, I have been known to simply use that field in conditional formatting to change the row color.) I also include this field at the top of the sort dialog to group the types together.
You can do the same thing with any kind of related data.
To explain jfletch's excellent suggestion in terms of your solution, you can create rates for an imaginary client called "universal". Where you now match a customer ID in a relationship to get just the rates for one customer, you use the ID for "universal" and the current customer separated by a return to get both universal rates and the customer's rates in one list.
You might consider using using a selection portal for this as this would enable you to segregate customer and universal rates into different groups should that be useful.