My team ran a sucessful pump day at our local field. We Called it Slowball Day. Had a great turn out (for pump) 25 players or so. We played on the speedball field back to back games street ball style. No teams just for fun. Everyone that attended had a blast and we were able to make the day inexpensive thanks to the field owner selling paint by the bag. We have another event scheduled this month. We pushed it as a great way to try pump. From first timers to seasoned players and offered our equipment up to try. From high end CCM markers to stock class phantoms and everything in between. We gave inexpensive prizes like gold, silver and bronze painted cans of beer microfibers and socks.
I would say start small. Creat a fun environment and people will show up.
If you happen to be in the 518 Albany NY area check us out. Capital Combat Zone. We also have a cool video I had trouble linking. It's pined in the link I posted.