Vary Length of outputSingleScan?

Hi,

I'm using Matlab to interface with an NI USB-6211 box, and I want to increase the duration of outputSingleScan. I thought I would be able to do that by changing the session's s.Rate, but that gives me an error if not set to 0. Any ideas on how to make this work? I'm already using both of the analog outputs for something else, and I'd rather not add an Arduino.

Thanks in advance,

Alex