i've been looking into the biki rom tunes (kind of diy rom tuning) and i think it would be quite possible to make those corrections by tuning it yourself. i've been reading about people tuning their cars to run a lot off of the tps and at you can do that at idle, and set it up so that once the throttle moves off of idle then it starts reading the mafs, or the map (which isn't used much by the stock ecu tune) or whatever you want. you could make the car run completely off the map sensor if you wanted. there are a lot of options with this setup but then again it involves a lot of work on your part because it wont just be done for you. as i understand it this is very close to the same type of tuning jwt or enthalpy provides for the stock ecu... there are other options other than rom tuning involving daughterboards and all kinds of other user tuneable setups... if you're interested check out
http://www.bikirom.com and read the forums.
http://ztechz.net is a good site about rom tuning, they provide a lot of info.