Perhaps a small muffin cooling fan aimed at the motor might add a little cheap insurance. Also you might find a way of attaching some old heatsinks to the motor without blocking any existing cooling holes. Sigh, if only you had a mill you could really make something : )
An old trick that some electric vehicle people sometimes use, is seating the motor to its attachment with heat sink compound.
I've seen people use small squirrel cage blowers and plastic hose to force cool motors.
Any of the above may void your warrantee.