My experiences here as a Diamond...
1) I tried the "new ACAQ account & online merge" process and it did not work.
2) I called the Diamond line and was told that an AC# was required and that it could not be processed w/o it.
3) I signed up at aeroplan.com and called the Diamond line back and was registered for the promo... it took my agent "talking to a supervisor", but it did get done. It was a courteous, matter-of-fact converstaion. "There is a promo... I want to register for it... yes, I know that this is for new acc'ts, but I am offended that I stayed 50+ times last year and get nothing, while new accounts get 50k points for four stays... 'please hold'... 'ok, you're signed up.' "
4) 24hrs later the retroactive bonus points were in my account.