But how do I get But How?

How can I get the But How? achievement on the Slaughterhouse map? The achievement states

In the Slaughterhouse job, get the armoured truck to drop without shooting at the wires on which it is suspended.

Shooting the wires doesn't appear to make the truck fall, and I've held out for 3 waves with nothing happening.

_{This is very similar to this question but that question pertains to Payday: The Heist, and the accepted answer doesn't have the relevant information (although the other answer does). Unfortunately, I wouldnt feel right about adding an answer to that as this is for a different game, even if the technique appears to be the same.}