On most acoustics there is a bone or plastic, bridge insert in the bridge, most are removable. Couldn't that be trimmed down a few thousandths to lower the action? Of course the strings would have to come off-- I was looking at mine on my cheap guitar, the guitar side of the bridge is flat, seems like one could flat file it, and measure it with a digital caliper to get the desired height. If you screw it up, just go get another one. I would think we are talking about an 1/16th to 1/8th inch move. I noticed the as the strings get closer to the nut, the clearance is closer---maybe thats where the truss rod comes in. I've heard of players "having their actions lowered", and it seems they take them to a luthier to have it done, so i just assumed it was a pro job.
I've never messed with the truss rod on my guitars, i've always felt that it was best left to a pro. I thought you only mess with that if you change the tension of the strings,i didn't know it raised and lowered the action. I know i did change the string tension on my cheap guitar,then got fret buzz, i took it to guitar center, and the tech adjusted the truss rod, and it went away. At the time, i didn't know there was such an adjustment on a guitar. Freakin magic!