This is the answer Bob Nelson shared with me a year ago last summer.

 

"It is certainly possible.  I have done it with my 2023 set.  You simply wire the field winding of one locomotive in parallel with the field winding of the other one, and the armature of one locomotive in parallel with the armature of the other one.  This is the same arrangement used in two-motor locomotives.  At a minimum, this requires three wires between the units, although I would strongly recommend using a fourth wire to connect the frames, which are the returns for the fields, to avoid currents through the couplers, and a fifth wire to connect pickups between the units, for better immunity to dirty track.

Rather than use connectors, I have simply routed the wires over the couplers, fastened with tie-wraps, so that the units are permanently attached.

The result is a real stump puller.  I can pull a dozen or so modern 2400-type streamliners at unreasonably high speeds with no trouble.