How do you profit from card counting without varying your bet size?

I guess you could always count from the sidelines and bet only in advantage spots. Not very practical I suppose but card counting in general seems pretty implausible these days

One strategy I know of is to have multiple people. One person sits at the table and always bets low, the other always bets high but only sits down if the person at the table signals to them that the odds are good (They can be off doing other stuff while the low-better is doing the counting, so they're not just standing around waiting).

You're still right though, the odds aren't that great and once they get a hint you're doing something weird you'll get thrown out.

That's what the MIT blackjack team did in the 90s.

That was the strategy used in the '21' movie with Kevin Spacey which was actually based on a true story!

Have someone else sit at your table when the count is good and bet high