freeship after discounts - code

[makenoiz]

Im working on fixing the age old problem of free shipping . If free shipping is offered (via Modules > Order Total > Shipping) for "order amounts" over xxx.xx it should only be applied after discount coupon has been applied and based on a the new subtotal that has the coupon amount deducted.. In order to do this. I need to have the variable $od_amount['total'] from ot_coupon.php available to function process() in ot_subtotal.php Can a zen guru enlighten me on how I can make this variable available to that function?

Also, if you see an error in my logic feel free to let me know.

Thanks