If you're really only doing symbolic algebra, there's very little mathematica can do that isn't commonly available as free software. This seems more like a solution looking for a problem. Even if this were necessary for some reason, you could locally emulate an ARM machine with qemu; it's not like mathematica can magically detect whether it's really running on a raspberry pi. (This would violate the license, but otoh, as it currently stands, running raspberry pi mathematica on a pi zero also violates the license.)
But really, one should probably either learn how to use Sage or fork out the $240 for a stand-alone mathematica license (or download it from a premier educational institution like The Pirate Bay).