It's curious to me how when a lot of discussions on remote workers, especially those negative to the idea, I rarely see mention of chat rooms, when I've used them at every single place I've worked remotely. Most of my career success is due to connections I've made on IRC. I don't think this is that rare of a scenario, see the #w00w00 folks.
In the era of "catfishing" where people can fall in love with people based solely on chat and online relationships, I think it's hard to deny it's possible to form meaningful connections online. Emails, conference calls, and video conferences aren't going to do it. If you spend 8+ hours a day "talking" to some one in a chat room, you can learn more than 15 minutes at a water cooler now and then. As well, the whole team/group can read the backlog and know what's going on with everyone else. No need to repeat the same story to x, y, and z.
I agree with what you've said about having some informal conversation during lulls on calls. Those moments can be very valuable. Another thing I've done on some teams is after a major release or milestone achieved, everyone grabs a drink of their choice and joins a group video chat and virtually goes out to the bar to celebrate as a group.
Lastly, one of the things I've done is occasionally send small gifts to other team members. As an example after explaining rubber duck debugging to a team member who solved their own problem immediately after asking me and wasn't familiar with the term, I sent them an awesome rubber duck overnight. (Total cost <$10 via prime)