CoTerm and standby permission are not tied together. They often parallel each other, but they aren't the same thing. So it doesn't matter if they are CoTerm or not for the sake of the standby. The agents can (and often will) do it in IAH, but I would not expect it to work by calling it in.

Also, to the OP, I can't imagine that it will help you all that much with the impending storm in that as soon as the first flight cancels many others will fill what few seats are left to all three airports. I wouldn't expect to see lots of open seats if there are any cancellations during the day.

Good luck!