I really appreciate everyone's responses. bganon, I was thinking the same thing: ignore the text in the PHB and "repurpose" powers from other pacts to fit the star pact flavor.
Don't be afraid to take some Con powers too if you have a decent con. I think people too often get tangled up in not wanting to use a given attack because they have "only" a 14 instead of a 16 in that stat. A +1 isn't a big deal.
I'd make sure my at-wills are using the best stat, but if there's an encounter power you like that uses a strong secondary score, why not take it?
Okay, it's decided then: star pact warlock, with a stat emphasis on intelligence and charisma. Given that, what races work well?
Pretty much anything works for that. Eladrin pump your int, Dragonborn and Halflings your charisma. Humans are good for any class, with that floating stat bonus that can go wherever it's most needed. Tieflings boost both of your primary stats, but the tiefling warlock is a bit obvious (if that bothers you).
I'd go with that halfling idea. That sounds like a lot of fun, and Second Chance is a great racial power. Small size doesn't bother you much if you don't depend on weapons, and the bonus against fear kind of fits with the idea of a guy who's delving into Things Man Was Not Meant To Know. The bonus versus OAs probably won't come up much, but extra mobility is occasionally useful.
The downside is that the other stat bonus, dexterity, would be doubling up on Intelligence. I'd probably dump Dex to an 8, thus boosting it to an average 10 with the racial bonus. You don't need strength much, and if you're getting into star pact, a low wisdom probably sounds like a good idea.
Overall, I'd probably go ahead with a stat buy like this:
STR 11, CON 14, DEX 8, INT 15, WIS 10, CHA 16
That's before racials; afterward it'll leave you with dex 10 and cha 18.
You could push the int to 16 if you drop con to 13, but that's up to you.