For bacteria cluster maybe, but with present and foreseeable technologies adjusting the fields in question to produce the right directed energy output to hit the sails seems unlikely to me. I am suprised they didnt consider having the whisp carry a maser within itself, and upon getting close enough, having pushed some distance ahead by rocket or the like. Said Maser would then direct its beem towards the whisp. the maser would be powered first by a battery, then as it got close the system's sun, solar panels