Hello,
What you are asking for is not a simple popup, it is a complete AjaxCart module, this needs to be created as a module to cover the logic behind it, I am willing to dedicate my time to get this acomploshed within the next 7-14 days maximum. and I am ready to start now.
I have over 9 years of experience in eCommerce Development and over 6 years in Magento.
Looking forward to hearing from you.
Sincerely,
Ibrahim Saleh
MageSuper, Ltd