OK, as Peter mentioned, you can sort of approximate creating a new playlist. ProtonVehiCROSS, here's a shuffle you may want to try.

shuffle0=By rating and least played,-play_last=2,comment=150000,random=5

This is based on a 1000 track playlist with an even distribution of 1-5 star ratings. You may want to play around with the numbers because it may be way off for your playlists. Try increasing the multipliers in the following way: (try changing comment multiplier first)
play_last - in steps of 1
comment - in steps of about 50000 to 100000
random - in steps of 1 to 5

Keep in mind that because of the way custom shuffles work, you'll get the following effect:
5 star songs for a while, then some 5 and 4 mixed, then some 5, 4, and 3 mixed, then some 5,4,3,2 mixed, etc. At the point you start seeing too many 2 star rated songs, you should re-shuffle. If you shuffle a playlist composed of only 5, 4, and 3 star rated songs, you should get better results.

Here's another one, but without giving any weight to least/most recently played songs.
shuffle0=By rating,comment=5000,random=1
Increase comment in steps of 500 to 1000, random in steps of 1 to 5

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As far as doing an album shuffle...
Since it's possible for 3rd party apps to add custom fields to tracks, you could create a field like "x-album" and have it be the same value for all tracks in an album. (Different value for different albums.)

Then you could do shuffle0=By Album and track order,x-album=100,-tracknr=1 to get a playlist of albums. Though not randomized.

Or shuffle0=By Album - Tracks randomized,x-album=32768,random=1 to get a playlist of albums with the tracks in each album randomized.

Unfortunately, unless you can get a random variable that can be seeded by, say, current time plus the value of x-album, a random album shuffle just doesn't appear doable via custom shuffles.



Also, just wanted to mention that I'm working on a Microsoft Excel spreadsheet that can use tracks copied from Emplode to list and graph out how the various shuffles would look like. If anyone is interested, I'll make it available when I'm done.