Summary:
Make provisions an unit stat, like morale.
Details:
More importantly, allow us to increase provisions by hiring troops from regions with food surplus.
Make it work just like morale: If we recruit troops from regions with high morale, we get high morale recruits, which may increase the average morale of our unit if it originally had low morale.
So, if we recruit troops from an rural region that's brimming with food, give us recruits with 100% provision, which will increase the provisions value of our unit via a weighted average.
Benefits:
Let us boost our provisions quickly via recruiting, instead of waiting for 10 days inside an rural region. Waiting is boring.
Possible exploits:
None that I can think of.