Not a chance -you have to pass Grade 6 in an instrument before it counts for UCAS points. It would take 100s of hours of practising to achieve this level (and then you'd have to find time to do the exam and get the result before the end of August.
However, you could take AS General Studies (although you need to check that this would be acceptable to the university as some exclude General Studies as an allowable subject). General Studies, as it sounds, is mostly general knowledge. You could do a few past papers and have a go. An E at AS would get you 20 points, a better grade would get you more.
To take General Studies you would have to enter for the 2 exams (there is no coursework) at an exam enter as a private candidate. AQA is the exam board most friendly to private candidates - see link to their website for private candidates, which includes a pdf of centres which may accept them. You'd have to pay to enter - the exam board fees are about £18 for each of the 2 papers but the exam centre will also charge you for admin and invigilation and this varies from centre to centre. It's certainly a lot cheaper option that paying for a lot of piano lessons.
AQA offers 2 different A level syllabuses - see links 2 and 3 for the specification, past papers etc.
If General Studies is no good then the next easiest(?) option is Critical Thinking. This is harder but has considerably more credibility with universities and so is accepted by most (if not all) universities, has no coursework etc. It is still based on general nous, but you do have to learn the technique to answering the questions. New link added for AQA syllabus.
I don't think FSMQ would be an option. If you are taking Maths A level then this will trump FSMQ and so FSMQ will get you no points. If you're not doing A level then you will find FSMQ hard - in many respects it is significantly harder than AS Maths.