For me, it it is adding an @IEEE.org as an alternate from: address in the iPhone mail client associated with a Google gmail account.
One approach is given here: http://modernerd.com/post/535350679/solved-gmail- ipad-iphone-and-multiple-from . It worked with iOS 3.0 but does not seem to work any longer.
An alternate approach is to create a fake pop3 account which sends through Google and uses a fake pop3 server account. I used the server mail.xyz for the server name. To avoid as many messages about the fake pop3 server not responding as possible, set it’s check mode to manual. Alas, in iOS 4, there will still be some.