As I've said, I've been able to slow it down 4%, but any scene change ends up with a slight fade due to the merging of frames on the added ones and it ends up overlapping at each cut.
Even if you can isolate the scene changes, the blurring of frames mid-scene will still ruin the flow of the video - it may not be immediately obvious, especially if viewed on a 60Hz monitor, but play it next to the original on a TV and I think you'll see what I mean. If I had to do this, I'd leave the video as it is and pitch-shift the audio, though that will never be perfect either, as it tends to introduce clicks and/or warbling.
DE