Hi,
The custom item or order data is not sent to PayPal by the PayPal plugin. So while you can do what you want with HikaShop, you would have the data from the custom fields directly in PayPal. You'll have to check with the order id on your website for the data.
Now if you really want to have the custom item field data sent to PayPal with HikaShop, it's possible with some code modification of the PayPal payment plugin.
If you want us to work on that for you, that's possible. You can reach us via our contact form to request a quote on that.
www.hikashop.com/support/contact-us.html