I believe Battlefleet Gothic had one or more scenarios of this type.  If I recall correctly (which I may totally not be), the defender couldn't use special orders during the first turn; translated to Starmada, this might mean that you couldn't use Evasive Action, Directed Damage, Emergency Thrust, or Vectored Shields before you're on full alert.  Damage Control, Fighter Launch, and Mine Deployment might also be up for restriction during this period.

Alternatively, you could go with "Until the attacker actually attacks a defending element, or moves an element within n hexes of a defending element, the defender's elements are unable to act (plot movement, activate cloak, launch fighters, fire weapons, deploy mines, &c)."  So the attacker gets to maneuver around a bunch, then makes a turn of surprise attacks (note - I recommend having the defender's shields up already.  Otherwise, slaughter on that one turn of shooting before they're up, game over), then both sides act as normal.  Nice and simple, with a suitable advantage for the attacker.  Could vary detection ranges for attacking ships vs. attacking fighters if you want to recreate the incentives that led to the use of fighters there the first time.