Yes it most definitely is, I dropped Chemistry and Economics and took AS and A2 Further this year, along with Maths and Physics. Self did FP1 and S1, did accelerated classes in D1 and D2 with the year 12s, then the rest in standard lessons(S2, M2, FP2, C3, C4) having already done C1, C2 and M1.
However do you mean you are currently half way through you're year 13 year, like myself? Because doing the full course in this time would not exactly be very easy at all