I'm sure this has already been answered somewhere in slashdot hundreds of years ago, but why not just go with "free as in freedom"? And perhaps use the word freedom insted of free when possible

Because freedom isn't free!

But in all seriousness, "free as in freedom" seems fine to me but it is replacing the already unambiguous "free as in speech". You're still stuck with the sometimes-confusing "free as in beer" and they're still cumbersome compared to gratis/libre.