You cannot fit more than one tire in the trunk. Here's how I fit 4 tires:
When going to the track I just mount my drift tires before I leave. Now that I have R-Comps, I'll prolly have the WRX play chase car. Here is the recomended way for those with only one vehicle:
In case you didn't notice, you can get everything for the S2K. Seeing old threads on stuff for cheap that I missed out on makes me sad:
http://www.s2ki.com/s2000/topic/5212...tail-for-sale/