Very unlikely that you can add more spacers under the stem unless you have a spare one above the stem that you can move around. You may be able to flip your stem upwards (if not already). Otherwise you need to get a new stem.

I agree with the other poster that if you're thinking about that many spacers, you really need to re-evaluate your riding position and/or body strength and fitness level. An inch of spacers is OK, but 2 inches indicates that the bike doesn't fit you.