Brief answer is take a look at using interfaces. In case you are not familiar with the concept

1. An interface is used to declare an intent to provide certain services
2. By services I mean methods and properties
3. Having defined your interface(s) you must create classes that implement the interface(s)
4. You have a choice of starting with TInterfacedObject or TCOMObject - an oversimplification but enough to get you started
5. Delphi does not support multiple inheritance - fortunately - but you can get a classs to implement more than one interface

Just how easy or hard this is depends on how you see your project growing. If you merely want flexibility for your own future needs it can be quite simple. If on the other hand you want to provide a well documented API that others will be able to plug into and extend you will need to do more work.