It's probably more trouble than it's worth. I believe there is a way to use a gcc cross-compiler from the NDK (native development kit) that generates java bytecode from a c source, but then you may have to learn an API to interface with it etc.
In short, if you make the Java part small, you shouldn't have significant performance penalty, and you can use the cross-compiler.
Google Dev has a good video explaining the whole situation.
(The first portion anyway, which explains why C code can't run directly on the android OS)