I'm not seeing the issue in the first place. (Maybe I'm missing something?)
The party splits in half and each half takes one maneuver in opposite directions, right?
The party starts at Short range to one another (or Engaged, but since it doesn't cost a Maneuver to disengage from friendlies, there's no difference here).
The first half of the party takes a maneuver which moves them away from their starting point. They are now at Short range from the other half of the party, which has not yet moved.
The second half of the party takes a maneuver which moves them away from their starting point, in the opposite direction. They are now at Short range from the starting location, and 2 Maneuvers (Medium Range) from the other half of the party.
For the party to rejoin into a single group, 2 Maneuvers would have to be spent, as expected.
All of that said, 'Zones' are probably the cleanest way to deal with the issue of Range Bands on a map. The Zones can even vary in size based on a number of factors (limited entry/exit areas, general clutter, etc.).