ahh, okay - I missed that point -.-
So then I got a got Alternative:
U can research the Ability:
"Comradeship engages"
That means, when ur troops got casualties, then the surviving men rescue their wounded comrades and carry them to the HQ, where they become the typical zombies.
To order this, u can implement a secound Retreat-Button, like the Brits got (Escape to Captain...).
When u now order the "Comradeship engages"-ability, the retreat-speed gets reduced. Everybody can carry 1 wounded comrade. When there are more survived then injured, the guys without a mate on his back help carrying the others.
So, for example:
The Retreatspeed ist only 0,6 with one guy carrying one comrade.
Now there are two, who carrying one comrade so the retreatpeed only got decreased to 0,75. (just for example, the real balance can get later =) )
Hope u like this way ^^