1: Buy a '95 Impreza L (One that is already leagal in the US).
2: Strip the L down to a shell (leaving the peices with the VIN).
3: Reassemble car using all the WRX pieces.
Now you have a legally registerable Impreza (because of the VIN designation on the body shell) that has been converted (rebuilt, whatever) into a WRX.
The old WRX body shell can be sold for scrap, as it's VIN would never allow it to be registered in the U.S.
Think of it this way, you would be driving an Impreza L...with a WRX drivetrain swap, interior swap, body panel swap.
Tuning the engine to run on 93 octane and pass emissions will be your only hurdle.
Hope this helped
P.S. I'm considering doing the same thing to my wife's '95 L...