I'm kind of excited, because this is the first really useful thing I share... so, here it is:
My starting situation: in my live sets I usually run two instances of Ableton Live, in which I load different live sets. I then route Live's output throguh Soundflower to a simple mixer built in Max.
The most uncomfortable issue of this setup is the need to switch windows from Max to Live in order to change set, then back to Max to mix audio between the two audio sources, and then back to Max to play the song.
With the patch above, I can fill a single umenu with all the Live sets contained in different folders inside a parent folder (The hierarchy is: "Main LiveSets Folder/Project Folder/Live Set").
I managed to get the [folder] object to look for .als files thanks to this link: http://revolution.byu.edu/helps/file-creatorcodes.php
(actually, you can get creator codes from the Info.plist in a Mac OS X application bundle, so this trick can be useful for creating personalized menus with custom file formats), temporarily add the live sets' paths to Max search path, and then a little Applescript sent via the [shell] external by Jeremy Bernstein https://cycling74.com/download/Share/JeremyBernstein/shellUB.zip
did the rest.
Now I just need to avoid Live asking me to save changes to the current Live Set before opening the next one... but I couldn't wait to share this!