Those useless AT guns...

[Volcano Man]

Also, the question itself does provide an answer. "What do you do with all those 45mm AT guns in 1944?" Hmmm.... lets see... ;)

What they are good for is stacking them with infantry on objectives or on key terrain where the guns can provide assault defense in the form of yet another unit that must be disrupted before the hex is taken. These guns provide very little assault factor, but they can be difficult to disrupt. They also have a moderate anti-infantry capability of course, when you fire the entire stack of infantry with the AT gun at enemy infantry units. Other than all that, we can officially say that they have outlived their "prime" and were in use long after they have lost their effective AT capability, unless you run across some PzKw IIs or Pz 38(t)s in 1944.