There is actually another option. I think it hasn't been mentioned because you mentioned your flight is operated by LH. However, looking at your flight times, it looks like you will be flying out of SFO-FRA. The 7:05 flight is actually operated by UA, so this would work. You can book into economy and waitlist for premium cabin. They will deduct the premium cabin amount, but if it does not clear, you get the difference back. It should be 57.5 miles for one way in business. More about it here:
http://www.flyertalk.com/forum/unite...s-issues.html#
Also, unlike domestic flights, r/t to europe are usually less than 2x one ways. And often less than a single one way!
You can't book your return yet, since the schedule hasn't opened, but looking at some other dates around then, it looks like the r/t would be $1535 pp.