Yeah it needs a source playlist.
Here's my suggested workaround
1) Make a playlist called "Today"
2) Set Party Shuffle to use the playlist "Today", with number of queued songs set to "0".
3) When you feel like listening to a certain artist or something, clear out the current songs in "Today", do your search for an artist or album and drag all the songs into "Today"
4) Go to Party Shuffle and click play.
Now it'll randomly play from your Today's picks. And if you want some other song, just find it and drag it into "Party Shuffle" and it'll queue up in the Party Shuffle list.
(ps. Of course if you have a playlist you like, just direct Party Shuffle to that playlist and click play. Then drag other songs onto "Party Shuffle" for them to queue up in preference to your standard playlist songs.)