Er…. I may be a bit rusty but I still know the hangdog rule so you clearly can’t do that without going via Embankment and that’s red blocked from Onzadog’s move.
Wait a minute, wait a minute, wait a minute.
You’re right of course, but you forget I picked up a black token right at the start of the game. The black token explicitly trumps the red block (see “Russett’s Gambit” in Appendix B) and opens up the entire Northern Line. From there, as you say, it’s trivial to change at Embankment for MC.
To be fair I should specified that I was playing my token, but I presumed that it was fairly obvious what I was doing.