T.T.F.N: Prologue (T.T.F.N. 3: The Beginning, perhaps) could possibly take place before T.T.F.N. 2 (and thus, indirectly, T.T.F.N. 1)

It would probably feature Luno as the playable character, going through childhood as he is pestered daily by his brother Solvice.  

It'll feature the same gameplay as T.T.F.N. 2, as Luno explores a game-world. The amount of game overs in the game gives Luno the idea to eventually exact his revenge on Solvice for being mean to him. 

However, as Solvice and Luno grew, Solvice grew out of his childish ways and became more affectionate toward his brother. Luno, however, continued to plan his revenge. The game would probably end with the intro to T.T.F.N. 2. 

It's a rough idea and won't be coming to light any time soon.