Upgrading UA codeshare on non UA a/c
 

I travel in Europe as part of itineraries usually involving a rtw ticket or travelling both ways via the USA.
Often the flight continuing on from FRA or LHR has a UA number but is a codeshare on a non UA aircraft.
Is it possible to upgrade these sectors? Unofficially I have been able to do it twice on the day of travel if i have already had the incoming flight upgraded with miles or a SWU.
I remember reading here somewhere that upgrades may be accessed on the day of travel only but can find nothing official .
The signifigance to me is that,if upgrading is possible , then it would be worthwhile insisting that the continuing segments on say UA or BMI are booked with a UA flight number if feasible.
Does it matter ? Not all onward connections in Europe are the usual "business is virtually the same features as economy" -eg United Airlines 9106 is a LH a/c doing FRA-Cairo . So an upgrade would have its advantages.
Ozflier

There have been heaps of threads on this subject. Most of them are under the heading "Ugrading on LH" or similar (try searching "upgrade codeshare" and you'll get a ton of threads. Check out this thread that seems relevant.

The standard line has always been that there is no way to upgrade a LH flight with a UA number ahead of day-of-flight. You can request a printed SWU that is valid on LH for a standby upgrade and this can be used on a LH flight (as reported by FTers, but not necessarily LH and UA policy). A post by Weero in the linked thread seems to indicate that there is actually a way to use miles.