The taper will not hold it. You need the key. A used engine is probably your best bet at this point. A new crank and flytwheel will cost as much as a used engine, and you still have to do a complete rebuild on the engine.
If you ever do another flywheel removal, be sure to use the proper screw type puller and some impact to shock the taper free. This will get it off with no damage. Make sure it gets properly torqued and staked when it goes back together.
2004 Rebel 250, 2003 BMW K1200GT (roadburner), 2004 BMW R1200GS(all purpose),
1973 Norton Interstate (in a box in the basement)
1968 Triumph Bonneville