The simplest solution would be a binary option based on some sort of qualifier: either stand and fight (like at present) or retreat to a predefined place, executing a move command. Such a reaction shouldn't necessarily be limited to scouts though, as equally any other unit without AT weapons may wish to retreat, so we're really just looking at a more developed reaction to a Hunt encounter.
What could complicate that is a 'glass cannon' nature where a unit may indeed be able to combat a tank - if it gets in the first shot - but lacks defence so thereafter would withdraw quickly. Such a situation would be similar to the 'shoot-and-scoot' idea of taking a shot and then relocating, the only difference being that isn't the result of a Hunt command.
Also, this reaction shouldn't necessarily be limited to tanks, e.g. a walking scout team encounters a larger infantry force so withdrawal is the best response. It sounds like we need a configurable threat response based on several factors, activated during a Hunt or simply being stationary.
Which then implies that a 'React' instruction may be the solution, requiring choice of a few parameters, which may be triggered whatever the unit is doing. If the instruction conditions are set up then a Hunting unit could, say, stand and fight, take a single shot then relocate, or relocate (flee) immediately. A stationary unit could do similar, e.g. an ATGM team would take the shot and then relocate.
As Hunt reaction and Shoot-and-Scoot both seem to be sought after, this would kill two birds with one stone.