Custom code for Zen-Cart: File uploader

My online printing company uses Zen Cart for the ecommerce / ordering side of things. The file attribute works great for files up to 8MB (php limit). A lot of customers are abandoning the upload/cart as they feel nothing is happening (ie a timeout). What I need is a progress bar / notification that when they click 'Add to cart' they get some notification/progress of the upload. Even something that just says 'uploading - please wait...' etc I have some code - but not familiar enough with ZC to implement it. This mod will take 10 minutes!