Loory -
Welcome to EM! Yeah, the auto-tranny will make things tricky, but the round Vibe nose should be amenable to a subtle grill block behind the honeycomb grille. I would spend some time here to see what other Vibe afficionados have done to their cars :
http://www.genvibe.com/
The emphasis will probably be performance, but you should be able to rummage around and find mods that fit MPG needs also.
Unless the Canadian Vibes are different, you must have roof-racks. Here is my "Hot Wheels Kammback" design :
You'd need a HUMUNGUOUS Post-It to make it work for your 1:1 scale Vibe, though,
.
CarloSW2