Updattion of Pricelist

Dear Experts,

I want to update pricelist by using percentage parameter. I know that i can update pricelist using Import/Export tab or in pricelist there is option of Factor.

But My client requirement is, he will update only Purchase pricelist(Say Pricelist1) & automatically Sales pricelist(Say pricelist 2)

be updated by plus 2.5% of price of Purchse pricelist.

Can i do this by creating form in screen painter.

If yes plz suggest any idea??

Thanx.