Hi Thomas,
you can create a custom se11 elementary search help and call the custom search help in your aet field get_v method.
You can set the product id and description of the product to be export from the value help. When u select product id in value help popup you can fill the product and description automatically in your assignment block.
you can refer below document, there are many threads in scn related to this topic.
How to provide F4 Help - CRM - SCN Wiki
Best Regards,
Dharmakasi.