What you have proposed won't put any extra btu's into the house, but it might keep the system temperature more stable.
It won't hurt to try...but you might have to make some other adjustments to keep the upper floor from getting too warm. Hot water will try to rise to the highest point in the system. Maybe try opening the flow control valve for the downstairs zone and leave the other one alone.
The next time the wind is roaring at your house walk around and take note of the drafts and cold spots. Spend some time sealing up the leaks.
Are you currently heating the house with the 700?