So do it right. Attach the new pipe to the old, get it fitted up nicely, and stitch everything in place. (On most sub-3-inch exhausts, I like to use two half-inch stitches each beginning about 120 degrees from one another.)
Drop the whole assembly, prep all 360 degrees of the pipe, and then make your weld. Yes, it takes a minute to hang the system again, but if you ain’t got time to do it right, you’ll have to make time to do it twice, as the old saying goes.
And of course, this carries the added benefit of isolating the car from the voltage the welder produces if not using the GMAW process.
This isn’t meant to be a comprehensive article, of course, but hopefully one or two of these tips are something you are already doing or something you might want to try during your next exhaust job.