There are lots of things that could be done, and they would have complicated effects on the game.
1) make it difficult to move/set up artillery. In other words, once an artillery unit is unlimbered, that represents its ammunition being unloaded as well-which would be very difficult to move.
So pick where you want the artillery to be, and assume its there for most of the scenario. This would enhance the value of self-propelled artillery pieces (which can move more easily). To balance that enhancement, those sp guns could have greatly reduced ammunition.
2) Make artillery more difficult to counterbattery fire. Now, we can watch the tracers from AA guns, and the rounds from artillery, leave the ground, and then shoot at that. This is implausible. But if you make counterbattery fire less effective, you make AA guns and artillery pieces more effective, because they are not at as much risk.
3) Longer aim times (as someone mentioned).
4) Less likely to kill, but more (or as likely) to suppress. In other words, the artillery would be used to suppress an enemy infantry unit, which would then require a ground (infantry unit) to be destroyed/caused to surrender. If artillery only fires, it would suppress an infantry unit (causing fewer actual casualties), but that suppression goes away. This would enhance the morale effect of artillery, and create more motivation for combined arms.
5) Make artillery less numerous. You may have the artillery necessary to dominate a small section of the front: but not enough to dominate the entire front.
6) Make artillery less powerful. Specifically, make the sexy, huge artillery (the giant railroad offmap guns, the 203mm guns, the nebelwerfers and calliope's) far far less common. Restrict artillery to the smaller mortars, and, for 'big' artillery, the 105mm guns. This would be more realistic (but less sexy).
All of these would have dramatic impacts on the game-dramatic impacts on the pacing, on the decks, on how casualties are caused, dramatic impact on how aa units are used and how effective they are.
Artillery is not a simple fix.
This thread is also pointing to other issues. Specifically, as has been said many times, WWII was still really an infantry war. Due to all the sexy equipment in SD:N, that is not the case here. There are a lot of vehicles (tanks, at guns, even halftracks with mgs, scout cars), there is a lot of artillery, there are a lot of AA guns, there are a preposterous number of planes. Infantry is really second fiddle to all the metal in the game. This makes for a very dynamic, 'fun', very interactive game. But its not plausible from a historical perspective. I'm beginning to realize that the whole division deck mechanism is simply incompatible with an historical model. If you try to fix artillery, for instance, you are going to cause a lot of problems with AA guns-which will really mess with the air game. And so on.
Steve