How to make Virtuemart to only apply discounts to sale prices

[bestrestusa]

Hey VM fans/users/developers!
I use Joomla 2.5.6 and VM 2.0.14

I created this website: http://bestrestusa.com

There, I have set up some custom fields that change the cost of our products. (for example: They add a different color or size)

The problem that I have is that the discounts we have set up are also being applied to these EXTRAS and we don't need/want that.

We want to know how to make Virtuemart to only apply the discounts to the sale price and not to the extras.

Thanks for your help in advance!
Jhon

[servlet]

I need to know too