Obvious solution: shut down the portal.
I don't think it's that easy. The Gamma Draconis - Nebula jumpnode was open for what.... weeks? And when the Knossos was destroyed the node remained stable (to it is a remote possibility that the Sathanas somehow is responsible for this).
The Sol - Delta Serpentis node is open for close to two years. Unless the gate has a mechanism build into it to turn the node unusable (which is very, very unlikely in my opinion), shutting down the portal won't do any good. They'd have to blow up the node, like they did with the Capella nodes.
On top of that the GTVA wants and even needs Sol. If anyone would be willing to close the node again, it might be people from Sol. Tough they would need to break through the GTVA blockade, destroy the portal in Delta Serpentis to make sure it works and then blow up the node (with all the anti-matter they have stored I think they could muster enough explosive force to destabilize the node).
But since neither the government nor the Fedayeen seem to be willing to cut themselfs off, there is noone who has even a remote chance of making that plan work.
And even if, by some miracle, that happens, it's only a temporary solution, since the GTVA can simply build a new portal, but this time they will probably have more support from the general public. Though the Vasudans might be even more against it.