Although not familiar with this model, a couple of ideas.
1. Add some styrene (.040" would be ideal but probably too thick, .020" might work) to the bottom of the end platform to artificially "thicken" it. Then drill and tap for the 00-90 screw. If you drill through the end platform, you would need to cut off the screw and camouflage it with paint. Use a Microtrains Underslung coupler to compensate for the lower mounting and (hopefully) get the coupler closer to standard height.
2. Just cement the coupler in place with your CA glue of choice.
3. Bite the bullet and drill through the end platform and secure the coupler and tapped screw with CA.
Maybe someone on here has more experience with these and will chime in.