Dynamic Playlist - random songs from multiple artists?

I'm trying to build a dynamic playlist where it will just pull from a group of artist I specify. The artists aren't grouped by genre or any other characteristics.

I thought I could just click select multiple artists in the "Only include tracks for selected artists" field in the advanced playlist, but that didn't work. I tried the random songs by artist, but I can't seem to find the separator for multiple artists (if it exists).

Does anyone know how I can do this?

TIA