So, since thumbs are up hindquarters with respect to the Gare Central preclearance facility, I have to wonder if it wouldn't be feasible to just have the CBP folks get driven to Montreal, board the SB train, and run 99% of the customs checks en route, with the border stop only acting as a backstop if there are a bunch of "problem customers" and/or for any secondary screenings (i.e. when they pull people off the train)?
I do realize that there's probably actually a good reason for this not being the case, but it did come to mind since the MTR-RSP time exceeds the scheduled stop time at RSP by a healthy margin (and vice-versa for the Lacolle stop as well). Even if you had to "bin" St. Lambert as a result (already in the cards with the preclearance facility anyway, so not a "real" loss there), this would seem to get you to a substantially similar situation sooner.
I do realize that there's probably actually a good reason for this not being the case, but it did come to mind since the MTR-RSP time exceeds the scheduled stop time at RSP by a healthy margin (and vice-versa for the Lacolle stop as well). Even if you had to "bin" St. Lambert as a result (already in the cards with the preclearance facility anyway, so not a "real" loss there), this would seem to get you to a substantially similar situation sooner.