assuming this is an old post (though cant see any dates on posts so not sure), but when i needed to find my cabin filter I actually found a video on youtube for someone replacing it on a Supra.
The G29 Z4 doesnt seem to have an awful lot of presence for DIY how tos online or on youtube, but you can be sure people are tuning and modifying the Supras, so always worth a search incase its part of the shared architecture.