good question. i remember when i enrolled at Usyd before going to maq that i could have done 2 majors, but i don't remember seeing anything similar at maq.
I think that it is unlikely that u can do 2 majors and finish in the same amount of time. there are a lot of units in psych and the 'electives' are most likely not enough units to be able to complete a second major. i guess you can do 2 majors but finish later.. sorry, not much help... :/