First off, if you do decide to upgrade, make sure you're booked on separate PNRs, otherwise EUA won't run.

I do most of my flying solo, but on the rare instances when I'm traveling with others who are non-elite, I warn them well in advance that there's a possibility I may leave them behind in coach. Of course, they're not significant others, so retribution isn't really a concern for me

The way I usually sell this to them is by ensuring they benefit from my other elite perks (i.e. I get them priority tags on their luggage, bring them through the expedited security/check-in lines, and if I have any on hand, give them one of my free drink coupons. I also bring them with me into the PC, but that's not an elite perk). Usually my friends are happy with that and understand that I've put in more than my fair share of time in coach to earn these benefits, though I do get teased and made fun of...a price I'm willing to pay in exchange for sitting up front (I'd like to think my friendships are strong enough to survive leaving someone in the back of the bus! ). I haven't flown with a companion since making gold, but I suspect the possibility of a companion upgrade will make things a much easier sell.