Originally Posted by farrish11

Unfortunately you'd have to go through DFW because there's no DAY-NYC flights.

Sample:

AA DAY-DFW 861m
AA DFW-LHR 4750m
BA LHR-CPH 610m
AY CPH-HEL 556m
AY HEL-JFK 4117m
AA JFK-DFW 1391m
AA DFW-DAY 861m

= 13146m = 90k AA miles in Y, 115k AA miles in J

You'd be better off finding another way to NYC and starting/ending your trip there...

AA JFK-LHR 3451m
BA LHR-CPH 610m
AY CPH-HEL 556m
AY HEL-JFK 4117m

= 8734m = 60k AA miles in Y, 80k AA miles in J

Of course, you could also use an AA All-Partner award to CPH on the first routing I listed for 60k AA miles in Y, or 100 AA miles in J. Of course, an All-Partner award would let you have stopovers in JFK or DFW, but not in HEL or LHR. With the Oneworld award, you could stopover in HEL AND LHR AND JFK AND DFW, plus you wouldn't have to find your own way to NYC.