Try two one way awards, should be close to same price/miles provided you don't have too much time elapse between the individual segments. For example, last week I took an award flight with this routing: SFO-ZHR-TXL-STR-TXL-FRA-LAX-FAT-SFO. Originally I wanted a segment from TXL-NUR and then go back STR-TXL, but 1k desk said that they couldn't book that piece, hence the mod to make a "round trip" however messed up that routing might have been.