It does look like an object position, doesn't it?
But, as I put it in this answer (mostly about equatives, but they work the same as comparatives),
The problem arises when too much has been left out.
- I like Bill better than Betty.
- I like Bill better than I like Betty
or does it mean
- I like Bill better than Betty likes Bill ?
And what happens when you use pronouns?
So it could be a subject, though any good writer would disambiguate it by adding auxiliaries as necessary. (In speech it'd be obvious because the intonation would be different, mirroring the different constituent structure.)
However, the reflexive pronouns (that's what myself, himself, themselves, etc. are called) don't necessarily have anything to do with comparative. The major rule for using reflexives is that if the subject and the object are identical, the object has to be a reflexive pronoun. (There are several minor rules, as well.)
- *Bill likes Bill. (grammatical for two different Bill's)
- *Bill likes him. (ungrammatical only when him = Bill)
- Bill likes himself.
This is a useful property, which sometimes allows us to determine what the subject of imperatives is:
- *Look at myself!
- Look at yourself!
- *Look at himself!
and what the subjects of infinitives and gerunds and participles are, even when they're deleted:
- To know myself is the goal.
- Appearing humble while promoting yourself is difficult.
- Seeing himself in the mirror was always a shock.
So in this case, the proper use of a reflexive in a comparative clause depends on what's being compared, rather than on the comparison itself. Different structures can produce different reflexivation profiles. These two sentences don't mean the same thing, for instance:
- I'm searching for something larger than me.
- I'm searching for something larger than myself.
Note, by the way, that me is standard here. No native American English speaker would ever say I'm searching for something larger than I in unmonitored speech, unless they were joking. If they weren't joking, they'd still be perceived as joking, whether they got the joke or not.
The first sentence above, but not the second, could likely be continued ... so that I can hide in it.
I.e, it's more likely to refer to a physical object, and the comparison is more likely to be a physical comparison; and it's less likely to be metaphorical than the second, where "something" means "some mental/religious/spiritual meme" and "larger than myself" means "emotionally overwhelming, enlightening, less narcissistic".
So, to wind up, reflexives in comparatives can come from several sources:
- Simple errors by people who think reflexives (like whom) are more formal and polite
- Obligatory coreference with a noun phrase earlier in the sentence
- Idiomatic distinctions, contexually determined, like greater than myself