Personally I abandoned a-levels to fly, and came out smelling of roses. I know this is only an option if youve got the money, and depends on lots of factors like the job market. I wont even pretend it wasnt a hard road, but its something to think about. All the time youre in School/College/University you wont have a frozen ATPL and therefore noone will give you a job.
Its my observation that those airlines running sponsorships ask for a level of acedemic achievement (e.g. A levels) in order that they can sleep safe at night in the knowledge your'e not going to waste their money failing the exams.
On the other hand I know of at least one person who got on to a sponsored course which asked for 2 a-levels, he had none but had already passed the ATPL writtens. Given that you'd have to do these anyhow, it might be worth giving this avenue a look.
If you are resigned to doing a-levels then how about dropping the UCAS points scoring crap like general studies etc, do 2 reasonable a-levels and look at doing an open study course for the technical subjects at the same time, after all, the dates that you take the exams for these will be flexible as well. Its also worth looking at doing a PPL at the same time. However you occupy the bulk of your time, the more flying you do the better!
regards and the best of luck!
HS125