i have seen a picture of a r33 with it done. the way that they had altered the piping was a bit weird though.
i think you would still get issues with stalling though, because as you lift off and the bov (even plumback) opens, there is going to be a rush of air go past the AFM, so it will richen up the mixtures a lot.
also the AFM would get dirtier easier, therefore give inaccurate readings. if you get a lot of blowby, or have a slightly stuffed oil seal on the turbo the AFM is going to get covered in oil, and won't read all the air going past.