Friend of mine I've inducted into the DC/MBNA/MilesandCash game ( ^ ) needs to go to EZE next year.

Outbound route is a no brainer LHR-FRA-EZE in LH F if he can get it (F terminal and limo etc etc)

Coming back he might want to stop in NYC, given that there is a UA EZE-IAD flight. Does anyone know if a DC Zone4-Zone1 redemption EZE-IAD-NYC(stop)-LHR would be permitted? It's not really backtracking but it's arguably not the most "direct" route?

If it is allowed, is UA C/F bad enough NYC-LHR to warrant doing LH NYC-FRA-LHR?