First, grab a DS flash card and install MiniVMacDS onto its root directory.
Once that's done, place the Mac Plus ROM into the "vmac" folder along with a System 6/7 install disk (you can make a blank disk image using Disk Utility).
Finally, turn on the DS and select MiniVMacDS. It will boot the disk images. From there, install (minimal) System 6 onto the blank disk image.
Ken notes that it's a bit pokey, but hey, this wasn't done for speed! Have fun if you try this for yourself. Thanks for sharing, Ken! We love it.