Another success! This time with a QFN package. Sadly my phone camera won't do it justice.
Like with the BGA flip chip earlier I sanded from the bottom with 120 grit sandpaper followed by 600 when I started to reach the leadframe. This works faster than you might expect. I stopped (slightly too late) upon seeing tiny metal dots outlining the shape of the die. Turns out this was a flip chip too, I accidentally erased a bit of the die during my sanding. This time however I torched it for a couple seconds, rubbed off what I could then let it soak in acetone for a couple hours then rubbed off the rest. No harsh stripper required!
Next time I try this I'm going to take pictures and document the process better. I guess I got a little ahead of myself.