Now if only I could up with a better name than "backlink=", but so far I've failed.
For what? Determining whether or not to display the backlink? How about "inline=false", meaning the <ref> tag isn't intended to describe an inline citation?
We seem to be agreed on what we want to do, it's just a matter of settling on a particular syntax now, and that isn't a big deal - all the suggestions given so far would work at least reasonably well.