You can also use the full SD fat API from the SD library that comes with Arduino. Its header files are include by the main SD.h.
On the other hand, maybe we can find a way to converge the simplicity of the SD wrapper with the power of the full sdfatlib (or beta-lib)? Probably the best way would be to discuss it on the developers mailing list: http://mail.arduino.cc/mailman/listinfo/developers_arduino.cc