And as you suggest, highly illegal. Well, maybe not illegal, but suspect: I wonder how the check-in agent would respond when one answered the question about "Did you pack the bag yourself?", or "Did anyone give you something to bring back with you?", etc. with a "Yes"? Have you checked to see if FRA airport or rail station have a check facility where you could leave a suitcase for a week or two? Most European travel centres do offer this convenience. Or you could just send the stuff back by sea post.