Look up MRA (Mountain River Adventures?). They do a paid shuttle van thing sorta like Downieville. You can probably just tag along with other riders so you don't get lost or broken off or something (there's only one fire road fork that isn't crystal clear, the rest is just following the marked trail signs).
Mountain River Adventures has a shuttle that will make a run to the trailhead of the Plunge with a minumum of 6 riders. The shuttle holds 12 so if you are lucky you can hook up with a group that has extra space for you to tag along. It departs the shop at 8:30 and takes nearly an hour to get to the pass. Call the shop. They are very helpful.
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