Did a quick search and could not find where this had been covered. If it has been - sorry to have missed the original thread.

Apparently, we can now upgrade a UA flight which is operated on US metal (a UA flight in the 2000-2999 flight number range) - provided it's a standby upgrade on the day of departure. I was able to deduct miles out of my account for my sister-in-law's upgrade from Charlotte to Denver on a UA flight operated by US (yup, US metal) (her company has UA as the preferred carrier, so she has to book through them). It's a standby upgrade - so if she doesn't get upgraded, I should get the miles back (we hope). The CP folks had to check through the rules to see if it was doable, and lo and behold, the standby route was there.

Of course, it all depends on if seats are available at check-in, which they are on her outbound, just not yet on the return. Not sure if we can upgrade using e-upgrades, but at least there is one option when you're forced to book through UA.