So, thinking about the scenario...
It'll be a long table, but the attackers only have to reach the middle, so that's the equivalent of crossing the width of a normal table. Probably ok in a 6/7 turn game.
Attacking is still hard though, and defenders are going to be well dug in with all the buildings.
Pete suggested that the allies get reinforcements, so how about this - any allied unit wiped out can come back on as reinforcements (this could include everything or just infantry). That means they can also outflank, but they come on via a random table edge, and still need to pass an orders test to come on.
All reinforcements are regular.
The allied players can choose to remove a unit before it's wiped out (so the germans can't reduce a squad to two men then stop targeting it so it can't come back on) but they have to do that as the unit's activation (so they waste a die taking the unit off).
And I think we've settled on the idea of using a dawn attack thing - so we start with night fight rules and roll for the sun to come up.
Does that sound right?