I think that would work nicely. A friend of mine does something similar with blue tape and I filed it away in "good technique to use" mental file.
I really prefer to put my sashing on as an L whenever I can and avoid what I call "long unwieldy strips" but unfortunately some quilts want some things...
On my recent Scrap Metal quilt, I wanted to show off the subtle stripe of the fabric and so I cut long pieces the long way of the grain. Because I know I already trimmed my blocks to be precise, I prefer to not measure at this step but to go along with the existing conditions so I smooth everything out on my ironing board and pin the heck out of the sashing strip which is cut slightly long, I mean like every 1.5-2", I pin down low with long quilting pins so they are never under the actual foot nor near the needle. I do this for each column. Then when I put the columns together I actually layout it out by where the seams at the end of the row match up to the row below it. Unfortunately, I didn't take a process photo at that stage (but I thought about it), will have to next time it comes up. I am trying to write up a tutorial on how to figure out the measurements long pieces of sashing for diagonally set quilts and took pictures related to that. Thanks for the prod on my to-do list!