If we have to stop short of the gate, due to not having rampers (which happpens quite a bit), I'll make this PA:

"Folks, we've stopped just short of the gate while we wait for the ground crew to get in place. Please remain seated with your seat belt fastened until the sign has been turned off. We also have an indication up here that some folks may not be wearing their seat belts, so if we could get you to go ahead and buckle those up for us, we'd appreciate it. Thanks."

The FA later tells me that she got a bunch of sheepish looks and heard lots of clicking.