Nice idea..... But seems like you might miss the angle of roll, unless the conduit is un-bent. Often I need to do this on a piece that bay already have a bend on it.
My method is a little less exacting but works well.
Take a small 4-6" scrap piece, and put it on the wall where the conduit you are coninuing would have gone. Mark the back, where it touches the wall on the inside, as a registration mark for the angle of roll. Then measure from the scrap to the outside edge of the KO or fitting that you're aiming for, for you're off-set distance, and mark where your tape touches the scrap. Then transfer this angle to the conduit for a center line, by doing this: lay your already bent or fresh piece on the ground, and put your scrap peice onthe end with the 'against the wall' mark on the floor, then transfer the 'where the tape touched' mark to the one you're bendin, and chalk-line the center line. Then line that up to you benders seam line, or dog leg knotch if you filed one. And bend your distance. DONE (complicated to explain but easier done than said)
Should also take a moment to explain the "dog leg knotch":
Take a scrap piece, and draw two straight lines on it bisecting the center line of the conduit. (One on top, and one on bottom.) And very important to do this exactly, as you'll use this to perminantly mark you bender. Then place it in the bender and transfer your marks to the benders seam line. Once on the hook, one on the top of the hook, and one where the conduit touches the radius of the bender shoe. Then cut a knotch with a tri-angle file, or a hack saw blade.
To use it: Lay you conduit on the floor, as it would touch the mounting surface. Then find the top, by holding a marker or pencil on the top of the conduit, and lock your hand, and side it down the length of of the area to be bent, or chalk line it. (extra careful not to roll the conduit while you do this. ) Then put the conduit in your bender with the line on the knotches for your bends. An old skool anti-dog-leg method.
"Well - I oughta....." -Jackie Gleason