I can see Gallia sending another force against Liberty and Bretonia while they send another force to attack while the main Gallic fleet is away, effectively cutting them off.
I can see this being an unofficial event being held in two places though a signup would be required to make it fair. GRN sends a large force to Magellan but finds a combined Liberty/BAF fleet standing in their way. Meanwhile Council/Colonials/ and BAF/LN volunteers make a push for the Tau's where a smaller GRN reserve fleet is on standby. Should the reserve GRN fleet be destroyed, said forces may circle back and attempt to crush the main fleet back in Magellan or wreck havoc in the Tau's and Gallic border systems .
GRN main fleet has a choice of either staying in Magellan and pushing into California if they destroy the distracting fleet or pull back and assist the reserves and ignore the fleet in Magellan.