Ah. Without using modules you are restricted to a single __DATA__ per source file. You could store a Storable serialized object there though and that would give you arbitrary complexity. Storable is in the core perl distribution so your customers should have it.

Or... if you need to package up a binary you should check out PAR to create the executable. Just keep in mind that you can't prevent (ever) your customers from being able to read your code.