Create Pop - Up Donation Form script to add to any button

Hello, I own and operate the website [login to view URL] - On this website visitors can quickly and easily download several free meditation audios. Currently when a visitor goes to a audio download page such as this: all they do is click and the download begins instantly. I want this to continue to happen, however as the download starts I also want the click to initiate a lightbox pop up that prompts the downloader to donate. A simple form they can fill in is sufficient, however the more attractive and appealing the donation form the better! Something minimal but could still have a small message from us such as "thanks for visiting, please considering donating to help us grow!" etc. I am open to ideas. Currently my only form of processing is pay pal so the donation payment will have to be accepted this way. To let me know you have read this far please include "Donation Form to the beginning of your proposal. I hope this can just be a simple script that I can add to the button myself as I will be adding lots of new audios in the future. I edited the website myself from a wordpress script and the "button" is a simple image with a link to the download on my server. I need the button to double link to still auto start this download, but also pop up the donation form. Thank you for your bids!