Well - if you're not overly concerned about the engine, then you could get a fairly accurate read on the trans fluid that way - run it in neutral to fill the converter and the valve body, then check. It would still take you about 45 seconds that way, and the more I think of it, the more I don't like it.
Think of it this way: running an engine with no coolant at all puts major stress on the parts of the engine that have no coolant - however, when an engine with a full coolant system is cold, the coolant that remains trapped in the block still functions as coolant until the thermostat opens and allows the coolant to flow and itself be cooled in the radiator. No coolant in the block is really bad, all around, in my opinion. That's why in some manuals it is recommended that if coolant has been drained from the engine, you pull the thermostat, fill the block with coolant and reinstall the thermostat before running the engine.
