The LH itinerary did not work out. The FRA-TPE trip (codeshare as UA) is sold out at $360 USD at ATS. Would have loved a BOS-FRA-TPE/MNL itinerary, though.
Now checking UA RT BOS-TPE and a separate RT TPE-MNL. Called UA this morning to see if I can use 20K miles for a TPE-MNL RT, turns out such a trip would be 85K on Thai!