Well, you could bring in the excavation equipment to make room for those lifts for motorcycles that are mounted to the wall with a pair of Steel box beams anchored to the floor. The elevate a bike above the level you can easily park another beneath it. A different approach would be to install a four post car lift with a floor that could support the weight of several bikes. Move the 3-4 out from under the lift to lower the lift accessing the one you wish to rotate into riding queue. You gain some room to maneuver. Or rather than digging out, put a 2nd story over the garage if one does not exist...or build the detached man cave high bay garage workshop if your property would support.
There is always buy the huge garage workspace witha nice house attached or included approach, but...you live in California, land of outrageously priced property.
