Hi,
Ok, I see what you mean.
The issue is that you won't be able to change that without breaking the ajax uploader everywhere in HikaShop. So far we only use it for the custom fields and the HikaShop configuration, but we're going to use it more and more and you'll get in trouble when you update HikaShop.
Did you try to use the "custom text" custom field type ?
It allows you to display the HTML you want (so you could actually set in it an img HTML tag with the image) and you could then use the "display limited to" option of the field to display itself or not, like you do with the ajax image, but you wouldn't get all the javascript around it which actually allows the user to upload his images.