Why not! Good idea. I don't do many roasts with the hot air gun nowadays, but the very best ones have all been with this method. I like the oven though, my wife doesn't have a problem with the smoke and it is much more convenient. The oven compared with the hot air gun is very much like an E61 compared to a lever group: the first one is more forgiving, the second one is unbeatable IF everything works out perfectly during the process. First - more "set and forget", second, more hands-on.
Anyway, I have some problems prolonging first crack too. It seems to be very much a matter of bowl size/material in combination with heat gun effect. I got my favourite roasting bowl cracked for me some years ago, but the last one I bought turned out to be even better. It is a double walled steel bowl, size and distance between metal layers very much like your set-up, if I am not mistaken. Perhaps I should drill some holes in my inner wall
I try to keep first crack @ ~8-10 minutes. Haven't tried 500g, yet. Worried about getting uneven results, but if you say you can, I feel I should give it a go too.
Just like you, at or near second crack I let the beans coast until finished.