Firstly, play against TDM modpack races.
For additional challenge, I reccommend playing as a Pirate or Nomad under P&N
For the masochistic, try being a P&N Pirate while playing against TDM races
.
As a P or N, there are no holds barred: lie, cheat (no codes, obviously), steal, do whatever you can to survive.
You can also try playing as a neutral race:
- no colonizing outside your home system, but feel free to wage war outside your home.
Military alliances and Refuelling Starbases will help a lot.