I just discovered the answer...
The Microsft Sql Server/100/Tools/Binn/bcp.exe utility uses the following format when writing out a datetime2 value in native raw format (bcp options -CRAW -n):
If this value is a null then the single byte 0xFF is written out.
Otherwise:
A single byte 0x08 to indicate a datetime2 value
Followed by 5 bytes that represent the number of Ticks (100 nano-seconds) within the time part of the value. These bytes are written out in the order LSB -> MSB.
Followed by 3-bytes that represent the number of days since 01 Jan 0001. Again these bytes are written out in the order LSB -> MSB.