Dunno if this is from juansolo or not, but I did manage to track down this blog post which seems to address the question:
https://obsoletetechnology.wordpress.com/projects/studio-electronics/dc-dc-bipolar-power-supply-for-effect-pedals/
The tricks is a DC-DC converter, in particular a LT3467 chip (mouser data sheet). Appears to not be available in a thru-hole package, so tougher for DIY builds. But figure I'd share!
https://obsoletetechnology.wordpress.com/projects/studio-electronics/dc-dc-bipolar-power-supply-for-effect-pedals/
The tricks is a DC-DC converter, in particular a LT3467 chip (mouser data sheet). Appears to not be available in a thru-hole package, so tougher for DIY builds. But figure I'd share!