There was a JDM 5-speed STi. I believe it's the 97-00 variety. It can be installed, not sure what's involved. It's not generally available stateside. RWD option just means a little mod in the diff. It's incredibly stupid, but doable. Say goodbye to your other diffs, they won't last long.
BTW, the EJ25 is drive by wire and you have a drive by cable fueling system. If you really swap'd an 04 EJ257, you would have had to do things like change your gas petal, etc. Sounds like you're building a hybrid with EJ205 heads and EJ257 shortblock maybe? We generally call those "hybrids" not "EJ25".
2015 STi: Still Stock
04 STi, 04 WRX: SOLD