You could use this product.
"Digital Fuel Adjuster
Ref: High Performance Electronic Project for Cars – Silicon Chip Publications.
This unit is a huge revolution in DIY automotive performance. It gives you the power to completely tune the air/fuel ratio throughout the entire load range, at 128 load points, providing incredible mapping resolution and brilliant drivability. It uses the Handheld Digital Controller – KC5386, so there is no need for a laptop, and it supports both static and real-time mapping. It can be used on 0-5V and 0-12V signals, so it is compatible with all voltage output airflow meters and MAP sensors. It can also be set to work with 0-1V signals, allowing modification of EGO sensor signals. This unit has been extensively tested on a wide range of cars including Subaru Impreza WRX and STi, Nissan 200SX, BMW 735i, Lexus LS400, and Nissan Maxima. Kit supplied with PCB, machined case, and all electronic components. Kit requires the Handheld Digital Controller – KC5386."
http://www.autospeed.com/shop/category_579/browse.html
You would have to buy that and the hand controller.