The issue I can see you having is the programming of the key, with the right equipment it should be able to easily do it, buy a unprogrammed blank from ebay ( make sure it is a complete blank including all the electronics) then using what ever is needed to program the key to the car and done.
The unit to program the key is the issue, I have just done this to our JDM 2008 Vellfire, the smart key was available from Toyota at a reasonable price ( $200 ) so I just bought that, I may of been able to get one from ebay but a/ I could get it the next day b/ 100% sure it would work c/ wanted to still have the abilities from the original remote ( twin electric side doors). I then plugged in my Gscan 2 went to the correct option followed the instructions on programming the new key.( took about 30 seconds) and was done. Seems simple enough except the Gscan2 is a $12,000 unit.It would program the key for your subaru, not sure if there is a cheaper unit that will do it.