11025kHz and framesizes question

I have been using the Speex NB mode with an 11025 kHz signal, without adjusting 
the framesize, and it's been sounding just fine to me. However I was wondering 
what the best way to make 11025kHz would be. I also have an audio driver that 
uses 2kB buffers, and the NB framesize of 160 doesn't divide evenly into that 
so I end up having to shovel tails of buffers around which isn't too efficient.

So I wondered if there was a clean way I could change the NB mode buffer size 
to be 256, which would be a little closer 20ms at 11025 but also be divisible 
by 2048.

Should I add a new custom mode to the modes array or should I mess with the NB 
mode? Any advice on what I should do with subFrameSize and the other parameters 
in SpeexNBMode (if anything) if I change the framesize to be 256?

Thanks,
Dave