(ET) Removing mower blade

[tbamc <tbamc gbta net>]

This concerns a Craftsman battery powered push mower, but perhaps would 
be similar for an ET?
The nut holding the blade to the shaft has apparently not been removed 
in years.  When I hold the blade, and turn the nut, the motor shaft 
turns with it.  I don't see any way to hold the motor shaft and keep it 
from turning. 

I thought of an impact wrench (no easy access to one) and heat (will try 
today), but if that doesn't work, are there other options?
Thanks.

Thon