connector email with attached documents (programmaticaly)

Hello All,
I'm using an email connector with attached documents and with UI form works fine. But I need send documents from an external API REST that I manage with a connector too. My question is how to populate my document variable programmaticaly with data that I have from my API REST. In there I have a JSON with the keys "title" (filename), "url" (bytes field), "data" (my content) and "hash" (hash content). Showing document content from my form I see for ex a JSON content like: [{"filename":"Mydocument.txt", "tempPath": "tmp_4443333399997777.txt", "contentType":"text/plain"}]. Is there a way to use a kind of key like "mybyte": "[mybyte content]" instead of "tempPath" when I send information from a form to contract variables or using an operation before the email connector be send?
Ideas, thanks a lot.

Walter