This is actually copied from Classic BattleTech, but I think it will fit well in this game too.
If a player has at least twice as many unactivated units as the other person then they must activate two units on their turn instead of one.
If a player has at least three times as many unactivated units as the other person then they must activate three units on their turn instead of one.
For example:
Turn 1:
Side A: 5 Units left, move 1
Side B: 8 Units left, move 1
Turn 2:
Side A: 4 Units left, move 1
Side B: 7 Units left, move 1
Turn 3:
Side A: 3 Units left, move 1
Side B: 6 Units left, move 2
Turn 4:
Side A: 2 Units left, move 1
Side B: 4 Units left, move 2
Turn 5:
Side A: 1 Units left, move 1
Side B: 2 Units left, move 2