It may or may not be "protocol", but one of the family members was on a motorcycle today. After a couple of us visited with him for a few minutes we got aside and talked and then went back and asked him if he would like to ride behind the coach with us. (We had two in front and two behind.) After the service he came and thanked us over and over for giving him the honor of riding with us for his uncle. 
I had not even gotten home before I received an email from him wanting to join the PGR. Maybe used judiciously, this could be a recruiting tactic. Of course, on this one we had like three controlled intersections and no busy freeways on the three mile trip from the funeral home to the cemetery. Making sure we visit with family members who ride might be an idea to help in recruiting new members.  