Think with me, are you tired to make a little fort in middle of battlefield, because you lose time and become an easy target? Is hard is not it?
I think i have the solution of this problem, pre constructions, you make you own construction with you 50 blocks or less, and save that construction with the "/save 1"
You have 9 spaces to save constructions, good is not it?
You just make you construction, (the game will know you put tows blocks) and when you finish, just write "/save 1"
But be warned, you can only make a construction with 50 blocks or less and the land need the space to you construction.
Example: building a 3x3 cant be placed in a 2x2 land,she will need more space.
Like the drag mode, when you are out of blocks, appears red lines, this advice can be applicable here to, in that case, the part that was missing from 3x3 to 2x2 field will be left with the red lines.
And one more thing to make a construction instantly, you go need a KS of 5, then you write "/load 1" and place it in the ground.
Hope you like my suggestion.