It's recommended that you do Calculus 1, it is not compulsory, so you don't have to do Calculus 1 concurrently
Alternatively, you could do Chemistry 1 in Semester 2, and Chemistry 2 over the Summer term if you really want to do Physics in your first semester. You'd still be able to satisfy the conditions for all your majors, because you will have done those 4 subjects you mentioned before the start of the first Semester in your second year, and as a bit of a bonus, you'll lighten the work load for one of your semesters in 2013 or 2014 cause you'll have one subject out of the way.
That's what I'm doing, anyway, cause I also wanted to do Physics in Semester 1 but I didn't want to give up a breadth
Or, you could just not do Physics 1, seeing as you've already done VCE Physics - and the GAMSAT only tests Physics up to to a year 12 level