This worked quite famously in VB6, see for example the first Blue Emu AAR on the Paradox forums. However I think in C# the NPR is able to distinguish between military and commercial engines and target the former preferentially though I haven't seen this tested in practice.
I tested this half a year ago and documented it in the "Saving Europa.." game.(
here) The setup was various different kinds of 7-9kt missile destroyers with the NPR faction vs 12x 7.5kt missile destroyers on mine (+2 beam defenders) and a large civilian armored freighter with CIWS on the other side of the engagement.
One might have expected the AI to prefer one or the other target, but though they seemed to somewhat prefer to shoot at the military targets
(..maybe just because there were more though?..), there were always some salvos also shot at the freighter, which he then absorbed.
So in effect, the tactic is not a perfect shield anymore, but definitely a useful pressure release valve. That is if it happens every time like this. Though I doubt it, the AI might have also considered the freighter a threat due to it sitting on the jump point escape route in the back. That seems like rather advanced reasoning however, so I am not convinced. Active sensors on the very close freighter could also have something to do with it.
Anyway, one way or the other, civilian shields can still be put to use.