Rules for Pricing (Enable % offset)

Hi All

I am working on a website for my company. We mainly wholesale, but going to branch off into retail as well.
I have created an e-commerce site with our wholesale prices.

I have created a wholesale authenticated user and a retails authenticated user. I want to assign a rule or rather have created a rule for anonymous and retail users to see different (retail) pricing. I am having a problem with the action part of the Rule listed below:

Event: Calculating the sell price of a product
Condition: User has roles...
Actions: Add an amount to the price
Is there anyway to change the ADD OFFSETvalue to a percentage(%)?

Please assist??