I guess it won't be easy especially if most songs are only by a few artists. To randomize it, I think you need to get the library (playlist) more even in the number of songs per artist.
I think I may have found a workaround.
In Auto-DJ, I click the Start DJ button which lists the tracks in the Upcoming Tracks section.
I have set 'gap before the same artist can repeat:' as 1.
I select all the tracks and add them to a new playlist.
I right-click on the new playlist and select List > Remove Duplicates.
The artists that have the most songs seem to placed further down in the playlist, while the ones with the fewest are more towards the top.
The same artist doesn't seem to repeat back to back, but skips 1 towards the end of the playlist.