If you get someone to clone as much as possible the design of the Hamer you like the whole balance thing should be sorted without having to design additional strap button extentions....
But say you find someone with the skills to make a 12 string (and they will exist), it's not going to be a cheap venture. But gets you your Hamer type looking 12 string...
How much would it cost to throw money at someone with a 12 string Hamer and convince someone to sell you one... if you ever move it on you might loose less that way.