In Feb, I got upgraded with a companion on the silver sweep. The gate agent wanted $50 for a go envoy upgrade for my 2nd companion (now on a separate PNR since I had to split for the sweep). We said no thanks to that and asked the FA once on board since there were several seats in F still open... the FA had no problem with the 2nd comp moving up with us. Maybe just ask nicely once on board if you have no luck with the GA?