Unfortunately there is not a simple way to do it with the current version of the activities.
One alternative is to get a draft with the Get Mail Messages activity, extract data from it (e.g., To, CC, BCC and attachments) and then send a new email with the Send Mail Messages activity.
Processed drafts can then be moved to trash with the Change Labels message.
Sample: GmailSendDraft.zip (3.4 KB)