One step further - I can generate a file in the right format to trigger the B_F. Now trying to come up with a useful R_P c___n with the very limited number of gadgets available.
Update: rooted. Man this box was hard, probably the hardest one I’ve done so far. Thanks @all and @sicario1337 for your help and encouragement along the way.
Awesome concept, thanks @guly and @freshness!