Okay, I'm going to preface this with "I know squat about Eberron." So if something I say doesn't jive with Eberron, please ignore me!
But what about an elf? The +2 Dex is definately a plus, especially if you go with any spells or feats that use ranged touch spells. This could give you an 18 DEX by only spending 10 points of your 28 point buy. You'd probably chuck another 10 at the CHA to get a 16 ... but that isn't bad. Your con would be bad ... but for 4 points you'd not have a penalty. That'd leave you 4 points to get your WIS and INT from being negative mods as well.
Of course, this could get you a 16 DEX by only spending 6 points of the buy. That's not a bad option either ... you could have a 16 DEX and a 16 CHA and have only spent 16 of your 28 points. Those extra 12 points could go a long way to getting that CON from being negative and maybe getting some intelligence or something.
Additionally, if you choose elf you get a longbow/shortbow proficiency. This could help in those combats where you are running low on spells. With a bow .. you have decent range, can stay out of the melee, and can actually be useful when not casting spells. Granted, your BAB is going to be bad ... unless you take a level of fighter and go Eldritch Knight. That combo can do some decent damage - at some cost to spellcasting, admittedly.
Anyway, i realize the elf concept is a longshot - but you've pretty much covered all the other races so there wasn't much to add there.
Anyone can play a gnome sorcerer or a human sorcerer. A halfling who is not a rogue is always neat. But I say go witht he elf!
