I managed to find a couple of pairs of huge stretchy, drapy fabric black pants that I could get away with wearing to work. My belly didn't exactly stay inside them, so I found some huge, dress-like shirts. I got by with 3 pairs of said pants. I figure that they were plain enough so as not to catch peoples' eyes and make them recall that I had already worn those same pants twice earlier in the week. I figured that if I had a variety of tops to cycle through, it would be okay.
I bought one of those belly support slings (not for this purpose, but sometimes it came in handy). Sometimes the tops of the pants would slide off my enormous belly, and they were too big for my hips. I would tuck them up into the sling to hold them on, and cover the whole thing up with a dress-like shirt. A problem with the sling I had is that the shoulder straps came in pretty close to my neck, so I had to be careful with the necklines of my huge, dress-like shirts!
It's a little bit humiliating to recall some of my tactics. I had never been pregnant before, so I didn't realize how huge I was until I look back at pictures. No wonder people were so anxious around me! By 5 months, I looked at least as big as most people with singles look at 9 months.