That always struck me as the solution: pump a click centrally to everyone and then everyone synchronizes to it. You might not be able to monitor but you've "jammed" and actually created music.
That's pretty much what Jamulus does: sound is mixed server-side, so you have a single point of reference (can be click track, can be drummer, can be sequencer...). You can even get a multi-track recording saved on the server so you can then adjust timings and give it a proper mix afterwards.
