Twilight check in for one pax on 2 pax booking?

We're flying from Gatwick next week and I had been thinking of upgrading to PE until I came across this site and found that not all PE is the same... useful info! shame... I was hoping to use Flying club miles to do it... using them for an upgrade seemed like good value at the time...?
Anyhow, does anyone know: We're going to check in online 24 hours before - was hoping to drop 1 suitcase off at LGW that evening during 'twilight'... but other passenger (2 of us on booking) can't make it in the evening... is it acceptable for me to turn up and drop off 1 suitcase under my name (both of us already checked in online) or do they really want to see all travellers on booking standing in front of them? If anyone knows for sure, I'd appreciate it so that I don't make a wasted trip to airport.
Anyhow, does anyone know: We're going to check in online 24 hours before - was hoping to drop 1 suitcase off at LGW that evening during 'twilight'... but other passenger (2 of us on booking) can't make it in the evening... is it acceptable for me to turn up and drop off 1 suitcase under my name (both of us already checked in online) or do they really want to see all travellers on booking standing in front of them? If anyone knows for sure, I'd appreciate it so that I don't make a wasted trip to airport.