Hey all, I flew with a Captain not long ago (we're NG drivers) and we were discussing this exact issue. He was good enough to volunteer that about a year ago he reached up during landing roll to deselect the autobrakes, and accidentally rotated the selector past the "off" setting and selected "RTO". Now, I believe the Boeing FCTM or Vol 2 says that RTO won't activate under such conditions,but PRESTO!, and the airplane was stopping way too fast!!!
In sum, can you do it, yes I suppose if SOP's allow, but as this particular Captain experienced, it might not be prudent. In addition, the potential for distraction etc by bending down and forward doesn't seem to warrant the effort.
Cheers