Can you do a philosophy text for your A level English NEA?

It depends on your exam board - a lot will theoretically allow any text to be submitted for approval, but you'd also want to check the support your school/college/etc will offer. I'll admit it seems unusual, but not impossible to pull off. Bear in mind you'd not only have to consider thematic application, but also the impact of individual bits - in comparison to Kafka! In short I'd check to see what your school says, but never say never.