Alternatively, just have the secondary attacks of rain of blows deal Strength modifier damage. That means all the bonuses you normally get to damage rolls don't apply to the secondary attacks.
My fix is to have Rain of Blows be a single primary attack that does 2W, with a single secondary attack that does 2W if it hits. (Although I haven't implemented it yet, I'm not running a home game at the moment and I can't change the power in any LFR games I run.)