I don't know your exact departure dates, but mid to the end of January I see quite a few dates where LX J is available from ZRH-PEK. I also see PEK-SIN on CA and SQ. Same for the reverse.

The return is easy - LX J PEK-ZRH has availability Feb 1. I also see CA J/SQ J from PEK-SIN to connect to that flight.

In the alternate, I also see plenty of LX J availability from HKG and PVG, where you can use SQ to connect from SIN.

So you can do something like this scamcharge free:

YYZ-IAD UA J
IAD-LHR UA Y (can't see UA J from any east coast city to LHR)
LHR-ZRH LX J
ZRH-PEK LX J
PEK-SIN SQ J

SIN-PEK SQ J
PEK-ZRH LX J
ZRH-BOS LX J (can't see ZRH-YUL Feb 1/2)
BOS-YYZ UA J

Something like the above would be worth the extra 50K.

EDIT: If your departure date is flexible to the 16th, I see SN J (Brussels Airlines) from JFK to BRU, then BRU to LHR.

EDIT 2: Again, if you're flexible to move your departure to the 16th, you can do LO J from YYZ-WAW, then WAW-LHR. If you're wondering, YYZ-WAW-LHR-ZRH-PEK-SIN is within MPM.