Disguise will work.
If it allows you to use Disguise to look like a specific person, it stands to reason that you can use it to perform a more general transformation, such as obscuring your race. To me, how much the look is to change, and how detailed he/she goes into making his disguise would determine the DC for the Check.
A Strix, as illustrated in the Advanced Race Guide, can be described as a winged Drow, so to look like a Drow would be a lot easier than trying to look like a normal Elf; and therefore would have a higher DC to accomplish the latter, since they could just put on a coat and shoes, realistically, to look like a Drow, but the Elf would be a lot harder due to their dark-colored skin.
Technically, there is the -2 to the check due to trying to look like a different race, but personally, I wouldn't worry about it too much depending on what they're trying to do. Say if a town was predominantly Human, and hated Elves, if a Half-Elf walked into town, he would be shunned, and it would be hard for him to do much, but if, say he pulled his hair over his ears, they'd all of a sudden look Human from that simple trick. I wouldn't make a player in that scenario take a -2, but they would still have to roll the check, or I would make suspicious onlookers make a Perception check to see it. The Strix trying to look like an Elf would, however, take the -2 in addition to the high DC from trying to look like a completely different race.