I was trying to solve this and this is what I ended up with.
Asset server which just chugs away in the background with no input from me. It doesn't have to be asset just one that will pick up changes automatically.
A script that runs periodically, finds all the flac files, shuffles them, then picks 200 random ones and overwrites a playlist called random.m3u
In the morning while I wait for the kettle to boil I assign random.m3u in "Home Music Share" to preset 1 on my remote control. (Wiim saves the list of tunes rather than links to the actual playlist due to some complicated upnp malarkey).
Now I press 1 on my remote and get random tunes. If I play something else then press 1 again it picks up where I left off ie the start of the last playing song.
Of course I could just press "shuffle all" on a client app but I wanted it to work with the remote because I'm not attached to my phone and I wanted the possibility of any tune (I have about 50,000).
Another way is to just play all your tunes on random on the server and use some broadcast software like icecast to play it as a continuous "radio stream". Then just connect to the URL when you want a full random selection.
There's probably a far, far easier way but the asset works for me and life is good