It's just a matter of playing with it. If you need to send 11 Bits with the MSSP, then you just need to send 2 byte (2x8 bits) BUT mask/set the extra bits with 1 or 0.

Have a look at MCP3204/3208 section 6
http://ww1.microchip.com/downloads/e...doc/21298c.pdf

If you really need speed, you want to use the MSSP port, case not, SHIFTIN/SHIFTOUT handle it.