I've never had good luck getting parking lot vouchers. One thing you can do assuming you aren't running paddles is have one of your group tow your bikes in from the campground. Just hook a few of 'em up to a pickup and 'ride' them to the entrance, once there you can take just the bikes in. As someone mentioned the local cops are pretty lax about most things, EXCEPT riding non-lincensed vehicles on the streets, so a lot of quads, dune buggies, and bikes get brought in this way from nearby campgrounds.
Just another option, my personal preference is to load up the truck and park it at the beach all day with gas, tools, cooler, girlfriend etc.