I can't give you any advice on the right way, but I can unequivocally tell you the wrong way.
In my troop, if the scoutmaster has a service project that he is personally in favor of, he will just schedule it, without consulting the SPL or PLC. He then will "require" everyone to be there by threatening to not advance them in rank if they don't show up. Also the service project will be on a day that already has another troop activity scheduled, and that activity was planned by the PLC and has been on the troop calendar for the past 6 months.
Yeah...my Troop is a 9 on the 1 to 8 ladd