By giving them a chance to download binaries, compiled and distributed by several trusted parties, like with GNU/Linux, instead of just single trusted party via single channel, like NOW.
And by distributing tamperproof checksums of the binaries in a public places, like news sites and forums.
Right now there is only one download location for the lazy and unwary - sourceforge,
but that is not required by design.
Actually there are several people on the forums who are working on doing exactly what you just advocated, I'd advise finding them and contributing.