This paper presents the Molen FemtoJava engine that is extended with concepts taken from the Molen polymorphic processor. This allows for the existing FemtoJava to be augmented with reconfigurable hardware with only a single extension of the bytecodes and thereby but still allowing the implementation of arbitrary hardware implementations. Therefore, computationally intensive functions can be moved to the reconfigurable hardware to improve their performance. Our experimental results on MP3 decoding, which is a common embedded application, can be improved by at least of 27% reduction of execution cycles with minimal additional hardware area (about 7%). Finally, our synthesis results also show that the Molen extension of the FemtoJava engine only required an additional 10% of area (in terms of FPGA slices).