In case anyone is annoyed with constantly trying to find a 3.3V source to power their J-Link / target, I put together a quick blog post about doing a two-minute hack to re-route 3.3V power externally, and make it easy to jumper it over to VTref:
Make your J-Link less annoying with this two-wire 3.3V power fixHope it's useful to someone out there!