The other hole in the fender can be plugged with a part from a 01 Impreza. The piece just snaps into the opening. I even used this piece on my GT!
I'm not exactly sure of the part number, but just go to your local Sube dealer and ask them to look up the part number. Tell them to look under the parts for the air intake of a 01 Impreza. The part is listed as a plug. I think it retails for $8, but subaruparts.com has them cheaper (I think). You still need to find out the part number, though.
Hope this helps,