Some body modification enthusiasts currently get significantly large silicon implants placed under the skin. The most common one appears to be synthetic horns,

Some body modification enthusiasts currently get significantly large silicon implants placed under the skin. The most common one appears to be synthetic horns, but large symbols in relief and larger abstract forms placed along muscles/against bone are also feasible. Note, when I say "feasible" I mean that no apparent reduction in function is caused by the implant. In this fellow's case, it might even be a good idea for him to encapsulate a wireless unit within a silicon sheath to avoid any kind contamination. That could increase the bulk of the unit considerably.