I've heard many people try, but no one has been successful.
In fact some have said that when they plug in aftermarket tools (like the DashHawk), they can't even get the fuel economy info. So I don't think the car's computer even has this info.
I hear that swapping the radio in a 3 will activate the function, as the 'mod' doesn't work for 2008s. A member here put a '06 radio in his '08 and now his trip computer works.
I highly doubt it, but I'm going to try a 2006 Mazda 3 CD/MP3 changer in my CX-7 someday.
If it works at all (trip or even CD/radio functions) I'll post the results.