Hello Silversaab,
I havent got the charts in front of me so can't give you a routing as such to avoid Brunei itself, but its worth remembering that their "territoral airspace" only extends 12 nautical miles from their physical shoreline (based on the '82 UN Convention on the Law of the Sea... are those yawns i can hear?!) so you can still fly in their FIR without requiring a specific overflight permit.
It is possible to go off airways to skirt around Brunei, just look out for islands and enclaves that are considered part of the Kingdom.
Cheers,
Buzzz