You need an ECU that is capable of throttle multi-map multipliers, which allows you to have the main fuel map and the ability to run additional multi-map multipliers (I'd say a minimum of six and usually every 10° of throttle position). It can then extrapolate between these for all the different throttle positions. On my turboed ITB engine (not S2000), I used Pectel T6 2000.

And ideally, you want an engine dyno to map such a set-up.....