the dreambubbles were spat up by horrorterrors, in the furthest ring; both concepts with no traditional association with place or time. all sessions access the same furthest ring, because there is just one pantemporal furthest ring; ergo, any session could theoretically access the bubbles.

This is basically my rationale. Feferi struck a deal with the gods to make it happen in Homestuck, but if she was able to do it, so could another player.