I know that you cannot have an attachment control in a repeating section...yet.
I've added my vote to the wanted feature list.
I'm wondering how you have got around this current limitation?
Normally I'd create a document set and upload all documents into it. However, I can't do that this time - it would all get too messy and require too much end user intervention and marrying up of document v question (why the document has been uploaded).
I've read the following post and added the control/code to my form. Yet, like others I don't know where the file would be uploaded/attached to.