Simple enough. If there is only one enemy unit, rush the HQ with your motorcycle (4 def, you will never die)
If there is two, you may need one support or two. You will need to take the second unit's HP low enough to do nothing, or to put your units in front to block their path.
If there is more, you may need to cage your motorcycle with other units to prevent it to be attacked.
I just saw I could try that, and I can't do it, 1000 signs maximum ^^