I'll preface this by saying that this includes one rather off-the-wall idea. I don't like saving Kymai when it seems so wasteful compared to the other foreign policy options that we sacrifice in its place, but if it's the people's will...
One of the big problems that we have for the salvation of Kymai is that one of the cities best positioned to save them with abundant ships, riches and local knowledge (Rhegion) is perfectly gleeful about the situation as it stands. So, what if we are able to reach a deal with Rhegion about this? Currently it's not in Rhegion's interests to help Kymai because every moment they aren't starved to death or invaded is one in which they're not picking up more of the share of trade that Kymai holds. But if we can change the calculus there, maybe we might not only get their approval for our own operations but perhaps we might even get Kymai to help?
For instance, one matter could be promising Rhegion assistance in other spheres that would make up the losses in trade. This could take the form of paying their merchants to harbor the refugees (and we could point out that as they are selling off their priceless yet inedible treasures for grain, bringing some over could be quite the lucrative venture in itself), strengthening our political ties to make the Sikeliote League more reluctant to bother them over Messana, assisting their paltry land forces to gain as much ground against the Sikels while they have the chance before being cut off, or even supporting their navy against the islands west of Lipara since those seem relatively empty for some reason. Most daring of all- we could propose to strike against Lokri Epixephyrii. Frankly I'm not sure if Rhegion is really all that into the Sikel land; it has but a small border with them, likely to be readily closed off by the likes of Mylai and Naxus, and the prize is mostly scrap of hill-country of questionable value.
Lokri Epixephyrii is another story; it has rich coastlands that have long been cultivated by Greeks which Rhegion would doubtlessly wish to secure, and the two cities hate each other. Furthermore, this is an ideal time to attack Lokri Epixephyrii; it has become diplomatically isolated. Her only distant friends of any sort are Sparta and Syrakousai. The former is not the best of naval powers to get to us and at any rate is locked in a titanic struggle with Athens, which controls via Kerkyra the safest approach to Italy by sea and maintains naval dominance about Hellas. Syrakousai is not in itself the strongest naval power (it relies more on Akragas for that) and she as well as her allies of Gela and Akragas are in a scramble to grab as much of the interior Sikel land as possible; to divert forces to the salvation of Lokri Epixephyrii would forfeit their potential gains. Waging war on the Sikeliote League and violating the peace established would bring the whole of Sicily's ire on them for the distraction in the middle of the war
they declared, and barring that they would have to use their naval power to send over their forces. This is an area in which they would be poorly equipped to contest the combined strength of competent Rhegion and Eretria, even with Akragas at their side! This is after a backdrop of promoting Sicily for Sicilians in the conference and the shearing of non-Sicilian ties, as well; for the rulers to support such a platform, they can't have all that strong of ties to an Italiote state without appearing as hypocrites.
For our part, Eretria has no love lost with western Lokri (the only city to refuse our offered proxenoi, spitting the slander of 'spy' with their forked tongues) and we are also allied with its other rival, Krotone, which would be pleased to see their demise. Shorn of allies, surrounded by hostile neighbors and threatened by the most powerful of the Italiote cities... how could Lokri Epixephyrii stand against such a force? This would serve to further isolate Syrakousai while it is unable to effectively respond and empower the balance of the allied forces against it, encourage our new ally Krotone with an act in their favor, serve as a clear example of Eretrian leadership to Italiotes AND serve as the chip through which we may purchase a more prolonged siege and liberty for a greater share of the people of Kymai. Perhaps an empowered Krotone and Rhegion may discourage adventurism against them on behalf of Thurii and the Sikeliote League, as well.
@Cetashwayo, would this be a reasonable option? Or would it appear that a long day at work has addled my senses?