Nylon is the material of choice for flag clips as it's not as susceptible to the elements as some other plastics. In addition, it has a pliability that reduces, or in this case eliminates additional mechanical parts as in the latch.

Print in Nylon - For additonal information, see: http://www.instructables.com/id/Combination-CNC-Machine-and-3D-Printer/

Then Cut through the slim side (as shown)to make a pliable spring/latch. Attach and raise!