For the most part you'd need to do a couple refluffs ... to be a "little green man" you'd need to decrease the hobgoblins side to closer to goblinoid. Similarly, you may need to change rods to look like orbs.
Stat wise you can have good charisma and constitution, and intelligence is always a nice last stat. It's whether you want to start with a pair of 18's for con/cha, but low int, or if you want to go for 18/16, with 14 int [and 13 str]. You could go for even higher int, but at that point you are pretty much giving up half of your attack options.
The one good thing about going with say 18 con and 16 charisma is you can have 14 int and 13 str. This lets you get into chainmail/scale armor ... which fits well as a sort of space suit type armor [not to mention being functionally useful]. Con is your main stat for at least one of your at-wills, and probably eldritch blast unless you end up with higher cha than con.
Power wise, well, your at wills are set in stone.
Level 1 encounter: For con based, you have to pick an infernal power. This isn't so bad, as either your charisma isn't as good as con, or your int isn't very high [or both], so the starpact bonus isn't that great on dreadful word. Diabolic Grasp as damage + sliding probably fits best as some sort of "ray gun" effect.
Level 1 daily: Flames of Phlegethos similarly fits into the ray gun idea for the attacks
Level 2 Utility: Ethereal Stride ... because teleportation seems like an alien trick, the rest of the PHB dailies not really fitting as well
Level 3 encounter: Both frigid darkness and fiery bolt give off ray gun type effects, with frigid darkness having a benefit when used with the star pact, and let's you mix things up instead of going all fire with infernal.
Level 5 daily: Avernian Eruption is probably easier to fit into the idea of alien technology, although Hunger of Hadar could be some kind of swarm of nanotechnology. Crown of Madness could be reflavored to be some kind of mind control ray.
Level 6 Utility: Shroud of Black Steel could be the space suit's other setting [for actual use in the vaccuum of space].
In general, a tough, smart and charismatic alien could make sense. Some of the darkpact powers may be useful [and there is a TON of extra starpact stuff in an issue of Dragon that could be helpful as well].
