Hey ash, using the slimfast on DDs is a good idea & if you want to stick to the slimfast plan, just add to your plan an extra 4 - 500 cal meal on a UD. If doing <500 DDs seems too much or too little even lol ..start off @ 700 ( you could fit in a couple of shakes & a bar for that, then reduce it by 100 a month until you get down to the juddd calculator numbers.
I feel you on the bingo wings if I flap mine too much I'd be mistaken for an Ostrich, so I'm going to start some gentle weight training.