You search for your trip as two one-ways. Normally the sum of both legs will be more expensive in terms of total fuel surcharge, but I have found the opposite as well. Plus the surcharges may be asymmetric, i.e. very cheap in one direction and overly expensive in the other direction. In that case you could buy the expensive direction with miles of another program.
HTB.
Interesting - I will try that out too.
Thank you.