As for the "Give Ground" command, you can do that fairly easily by grouping the center of your army (G key) and then holding ALT and left clicking away from the enemy.

I know the technique that you are talking about and it is also harder to use than I first thought. Of course, it is not difficult ordering the troops to fall back, thats the easy part. The problem is that when you do that you are presenting two weak flanks to the enemy (ZZ):

ZZ ZZ
X X
XXXXXXX

If the enemy is stupid enough to follow your center then you have him. Close your flanks (ZZ's) around him and he is surrounded like at Cannae. But if he doesnt follow your center you are in trouble. Now he can either blast he crap out of your forward ZZ's with ranged fire, or he can swarm one of them and force it to rout (with the rest of your army taking morale penalties and your plan backfiring). If you let him maneuver to a flank then you are in even more trouble (enemy is OO's):
O O O O
O
O O
ZZ ZZ O
X X O
XXXXXXX O

It's a risky tactic, but as Hannibal proved-- it can work. It seems to work best against over-eager chargers.