This may be a bit less plausible than some answers, but how about music?
La-la, la-la, la - la-la, la-lah-la-la-la lala la la, la-la, la la-la, la-la-la la-la, la-la, lala-la la -la -la -la lah
So, when referencing music (tunes, rather than lyrics), some filler needs to be used, not for inherent meaning but just as a vehicle for the tone, pitch, and rhythm. The fact that it may be, essentially, pronounced differently (la, vs lala, vs la-la, or Lah) shouldn't make it a different word, because it itself doesn't have its own meaning, it is just filler, and the people using it wouldn't think of it as different words. Of course, to be the go-to for music, it (whatever filler it is, lala or dan-dahn dan, nana-na or something) should probably also be a word, perhaps a filler or emphatic or placeholder, since they tend towards short easy sounds anyway.
If a culture is pretty musical, and also high-context (where people are supposed to notice and reference, rather than spelling things out), some filler word might end up being a substantial part of their vocabulary - because they are essentially quoting bits of songs at each other (well known ones, for well known meanings, or obscure ones when sure of audience) about like we use quotes or references, anywhere from in-jokes to obvious cultural references.
You would need to quote pretty often, to keep the percent at a third or a half of a conversation - but on the other hand, you can stack them up pretty much on top of each other, depending on how long the quoted music is.