If you want to, there is nothing to stop you holding the ND grad in front of the lens with your hand and moving it up and down. It's not ideal but possible. Saves on expensive holders etc. Easy if you are using a tripod though. I have seen various Heath Robinson contraptions with elastic bands and stuff in the past. None of which work.
I often shoot with and without just in case.
"you're looking at a whole world of hurt"
I don't have grads but to mimic them I shoot RAW and bracketed at -2 and -1 (or more). Then from LR you can load the original and an exposure into PS for the sky (whichever is correct), and use a gradient mask on the layer to act as a pseudo ND.