What if the front one is only a small fraction of the thrust at the rear? Would that be enough to "clear the path". Surely it would cost some efficiency but it may beat he alternative

Whipple shields [1] don't weigh much, and don't involve negative acceleration of any kind.

1: https://en.wikipedia.org/wiki/Whipple_shield

In other words the space-equivalent of a supercavitating torpedo like the Shkval [1], more or less an underwater rocket which creates its own gas bubble around the projectile by deflecting part of the exhaust stream to nozzles on the front of the device.

[1] https://en.wikipedia.org/wiki/VA-111_Shkval

In a universe where every action has an equal and opposite reaction, why not make those reactions argue about it?