[moodgiesanta]

If you have access to astral magic, Gate and Teleport are wonderful spells. They make reinforcing a lot easier. The nature spell Faery Trod (I think) opens a gate into a distant forest province, which, while not as useful as the astral spells, is still very nifty. Another thing is to build forts/castles/citadels/whatever in your outlying resource rich countries, although that can be expensive unless you have a cheap fortress. Using fast-moving troops is an obvious one, and using summon spells that can be cast in distant provinces is another. Lots of ways to do it. And of course, you can always just move your troops out, as you said, with expendable commanders (with some kind of leadership enhancing item) who do nothing but ferry troops to the exterior (and over time they actually gain experience, making them an OK emergency tool as well eventually).