I accidentally stumbled upon the right way to print custom size while using Photoshop. First, you put that custom size paper in the rear tray. Second, you select Print. Third, go to Print settings... Fourth, in the Commonly Used Settings, I selec...
I came up with a little hack. I stick my cardstock onto an A4 paper and it tricks the printer into thinking that I am printing on an A4. You have to know where your image is going to be printed on that A4. I'm using photoshop so this is what I do....