Have been following this discussion with interest, here is how
I proceed:
 
I use template routing having made a template of 1/4"
plywood with a slot 1-1/4" x 4" the, slot is 2" from the top
The plywood  template size lengthwise is made so that
the left side will center the slot on the ends and the right side
will center the side slots when lined up with the corners
of the hive box,  the template is nailed to the
assembled box with two tacks. The router is set up with a 3/8"
straight bit and a template bushing. Two depth settings will
bring the slots to 1/2"depth, which is sufficient for me.
The box is held with one foot on the floor during the routing.
Moving the template is easy, you just pull it off and nail it again
to the next side using the same tacks.
 
Regards from Viktor
Hobby beekeeper in Hawkesbury, Ontario.