Special price for product in percent

Hi!
I searched answer for this question more than week but didn't find any useful information.

How I can set special price for product WITH OPTIONS in percent?

By default special price calculating by formula: but I want to change it to: i.e. if:
default price is 90$
price for options is 10$
and special % is 15%
product price with some selected option will be:
(90+10)-(90+10)*0.15 = 85$

I want to change functionality of specials because I want to do specials more simple and understandable for my customers.
For example I want to create Christmas selling with 15% discounts for some products, but I can't do this, because my products has options and discount amount (in %) will be smaller, if customer will choose some option.

I know that this problem can be resolved with coupons but this method is not simple and not clear (I must write somewhere in product description coupon code, how it works, because not all customers understand it, customer must add product to cart, add coupon and only then he will see a discount).

Any information will be helpful.
Thank you!

Hi
Did you found a solution on this??

There used to be an extension in the Marketplace that did allow to choose between fixed amount of percentage and it also has several other options like to what or which group (Set, Category or Manufacturer) the discount does apply...
You can try to contact the developer HERE. He does speak a bit of English but the site in completely in Russian (the email is the little cog gear, mid screen right side)

I'm sure there are other in the Marketplace if you spend a bit of time searching...
Maybe this one...

https://www.opencart.com/index.php?rout ... percentage