Plug & Brace
I noticed that if I put a beam on a normal plug brick that I can extend it out two voxels. It allows me to place a brace blueprint underneath the first beam attached to the plug (although it appears red so I know it won't build). This allows me to extend the beams out to three instead of two. When the bricktrons try to complete the task, they attempt to put up the third beam but they won't put up the brace, thus the third beam just falls (or collapses).