Personally, I'd like to not rely too much on Canon PCs. 

I like the artifact idea, though. Perhaps the artifact IS the pendant, given it seems to be a key part of Chrono Trigger? Plus, other than the teleporter freaking out, all the time travel until the Epoch is through Time Gates. The Time Gates, iirc, are the result of Lavos' presence and were always there, and they vanish when Lavos is killed. So we don't really need to have the teleporter so much as an accident involving the time gates.