If it's an auto, get an impact gun. You can try to have someone hold a bolt on the torque converter through the access hole to hold it in place. But really better to just invest in an electric impact gun, comes in handy for other work too.
Auto? Remove the flywheel/bell housing cover easily.
Bend a piece of hardware store Aluminum strip in a 6 inch piece in somewhat of a Z shape so end of z engages a flywheel starter tooth and bend keeps piece tucked into bell housing.