They do exist. This is a unit that takes info from the mass airflow sensor, modifies it & sends it to the computer. All of these perameters can be adjusted. Some people call them adjustable MAF. I know that they have been big with the turbo GN crowd. They make them for LT1 & LS1s. That's all I know about them though, If I say anything else, I will be talking out of my ass. Check it out.
http://www.maftpro.com/faq.shtml