Any way to skip tmp dir?

[ftab]

I keep /tmp in RAM so as to make it super fast to handle things like PHP sessions and whatnot. By default, pyxtrabackup started filling up my /tmp, but as my databases are in excess of 70 gigs, I don't have enough RAM for that to work out.

Do I have to specify a --tmp-dir (which will be basically on the same hard drive as the final destination of the backups, which I guess will make things twice as slow) or is there a way to have it write directly to the destination instead of going through a tmp dir?