Save the game, then buy a Specialization book from a vendor. The message 
"Specialization Unlocked" will appear. Then, load your saved game, and you will 
have the gold back that you spent for the book, but the specialization will 
still be unlocked.

When you first arrive at your party camp, you will see Bodahn Fennick, the Dwarf 
trader. Speak to him, and view his wares. You will find two Specialization 
books, Ranger and Templar. Save the game, then buy one to unlock that 
Specialization. Reload your game, and buy the other one. You will now have both 
specialties unlocked and still retain your gold after reloading your game again. 
This works with all Specialization books.