For a list that is appified, there will usually be 2 SmartObjects generated:

TestList - information about the list item

TestList Attachments - attachments of the list item

The 'TestList Attachments' smartobject will have read/list method that accepts the List ID as the input property and return the attachment(s).  It may be possible to create a reference for the attachments, loop through the reference, and upload each to the library.

There are also wizard that make use of these SmartObject under the cover such as:

http://help.k2.com/onlinehelp/K2ForSharePoint/UserGuide/4.7/default.htm#Thick_Client_Wizards/List_Item_Events/Get_List_Item_Attachment_Reference/Get_List_Item_Attachment_Reference.htm