I have used vice grips on the flywheel or flexplate, wedged against the block, pretty successfully in this situation. If the engine is in the car, you can do with with the clutch access cover removed.
I also have a couple of longer bolts used to reach well into the threads to get the damper started on; I pull it on a ways with the longest bolt, then go to the middle length bolt to pull it on some more, then put in the standard bolt to get it finally snugged and torqued.
Strive to get to the spec'd 135 ft-lbs of torque. That clamps the damper firmly to the crank, and that is needed for the damper to actually do its job of absorbing the internal crank vibrations.
