If you arrive and find a squatter with nobody aboard. What about digging some lines out, chucking out some fenders and rafting alongside, then tie to the ball.

When they come back, they can then FOQ. You may find they return a little quicker...

I recognise that the balls are not supposed to have more than a single 60ft yacht on. But assuming it's not blowing old boots...and it's for a short period of time...and you remain aboard until the offender returns...plus what is the actual load limit on the balls? An ocean going yacht like a Hallberg Rassy 55 weighs roughly twice what a Jeanneau 54 does...so if it can safely take one of the former, it can certainly take two of the latter.

*this post doesn't change my 100% negative view on BB btw!