how to add attachment adding functionality in custom aspx task form in workflow?

I have a workflow with several custom aspx tasks. When the initiator starts the workflow he/she has the possibility to add/remove attachment into the list by using list's item add feature. But when the workflow creates the tasks and assigns them to the performers there is no functionality to add/remove attachments, because they are custom tasks, I don't know how to add the attachment management into the custom form.

if you have any ideas or thoughts please share it.