How to build unsigned ipa

I have a client that insists I provide them an unsigned .ipa or .app file. I understand that an .app file is an unzipped ipa. They want to do the signing, and have done it like this before with other developers. How is this possible using Air? I have looked into methods of trying to unsign a signed.ipa but I'm not really having any luck. Anybody know? I can't be the only one. Thanks.