Your best bet if the boat has not been run on a long time is to get the bow as high as possible, pull the drain plug out of the oil pan, not the block and let it flow out the bildge in to a drain pan. Good luck.
Probably you're best bet. Depending on what oil pan and where the drain plug is, it could now be rigged with a fitting, valve and hose so next time all you do is stick the hose out the hole where the hull drain plug goes, open the valve, and wait.....drink beer whatever.
If it's an automotive pan, the drain plug is likely on the bottom of the pan and a triple jointed midget couldn't get it out. Then you are left to pulling the engine, as Ralph said, or at least up some, pulling the plug and draining into a pan or the bilge, or sucking it out the dipstick tube with a Motive like vacuum pump. You'd need that either way in this case. Hit Summit Racing or Jeg's up and search Motive.
Ray
Edit: Running on the hose, post some pics of what motor mounts, etc, you have. Should always disconnect the driveline from the engine, then hook the hose to the engine. Start the engine, then CAREFULLY open the hose water so water flows at very low pressure out of the O/B dumps or exhausts. Sometimes impossible to disconnect the driveines with some mount combinations, and what I HAVE done, is run a pair of hoses from another hose bib on the house, one up the intake and the other up the nozzle as far as I can get it, wide open. Don't do that in the driveway! You're gonna soak down your entire garage, house, anything nearby. If anything, point the rear of the boat at the neighbors house or the street doing it this way.