Once the siege is broken you should have plenty of time to research a safe
mass stone to flesh spell ...
I like this idea
I'd have wizard and cleric work out some cooperative spell, if possible. It would work like 'turn all
willing targets within x feet to stone' - as there's next to no combat value and one could add casting time and XP components it should be low enough in level to be cast repeatedly over the course of several days.
Then the cleric announces (after a
commune to play it safe), that by the grace of god X all those willing will be saved the ravages of hunger during the siege to come. Add rumour-spreading (rogue), diplomacy (paladin) and performance tricks (bard) as needed to convince the masses. Those not trusting in the cleric would be assured by the wizard, that everthing is going to work by arcane law and all calculations are correct (or somesuch).
After reasonable preparation (excavated tombs, reinforces warehouses, cellars, etc) you'd start working the magic. A city of wizards should get enough spellcasting power together to cast the ritual spell over all willing commoners and thus remove them from the equation. Then you can start on breaking the siege.
Serious props to Baron Opal for coming up with the idea, as mad as it sounds at first.
