How to add a "one time" weight attribute to total weight?

Dear All

Have spent quite a while searching for an answer to this problem, I'm sure others have stumbled at this hurdle but can't fine the answer, apologies in advance if I have missed the answer....I have successfully managed to add a "one time" price increase attribute which is not multiplied by the number of items in the shopping cart, but I also need to add a "one time" weight increase attribute as well (for the same attribute), however unlike the price the weight is getting multiplied by the number of items in the the shopping cart and not a "one time" addition, my attribute setup is as follows:-

Any advice, help or even look at this thread you stupid ***** gratefully received. Thanx in advance...

image can be seen here:- https://www.iss-com.net/attributes-01.jpg