I used to play with 2-4 pancake projects a day and always just (carefully) picked up the pancake (holding it vertically) and mated it with the flange in the vertical position. I would then place it on the horizontal tape machine (at that time I was working with Studer B-67's and an Ampex ATR-100) and drop the other flange into position (never using any screws and saving tons of time). If the machine was one of our vertical machines (Otari MX5050) I would pretty much do the same, but that required being a bit more careful because the tape could spill more easily. On the vertical machine I would mate the pancake with the first flange, place it on the machine and then place the second flange over the pancake. Once you get that first flange in place it's really quite simple in either format.