I was just thinking about this driving home today and figured I will order the Toyota badges from partznet.com. I've ordered JDM Nissan/Toyota parts (sometimes discontinued) through them in the past at the cheapest prices. That's how I feel right at this moment... but for some reason I have a feeling that, through some miracle of how Scion markets this car, I will want to keep the "S" by the time of launch.
Also, if there's stuff that makes it hard/expensive to convert the Scion into Toyota-spec, I won't bother. Example: JDM Skyline is RHD so any USDM G coupe rebadged to a Nissan Skyline does not look like a Nissan because
1) It is LHD.
2) Steering wheel, seats, and interior usually still have the Infiniti "Mt. Fuji" logo.
One would literally have to spend thousands to aesthetically convert a USDM G coupe to a JDM Nissan Skyline.
BTW, the oval shaped "T" or "S" emblems are usually secured by adhesive + 2 pegs to align it into the body. Other emblems (such as "FT-86" or "FR-S" on the rear decklid) would usually be tacked on by adhesive only. So, with a hairdryer and floss, a re-badge should be easy.