go to walmart (or hunting store) get a big game hoist, the one with blocktackle rated for 700-1000 pounds, secure it to a large tree branch, lift the bike, back your truck under, lower and secure the bike...
or use 2 ramps, first ramp is tailgate to ground and the second ramp goes midway of the first ramp to ground.
really depends on how hillbilly you want to get...