This works, most of the time:
(prerequisites: have reptyr and tmux/screen installed; you'll be able to find them with apt-get or yum, depending on your platform)
Use Ctrl-Z to suspend the process.
Resume the process in the background with
Find the process ID of the background process with
You'll see something similar to this:
+ 11475 Stopped (signal) yourprocessname
Disown the job from the current parent (shell) with
tmux (preferred), or
Reattach the process to the tmux/screen session with reptyr:
Now you can detach the multiplexer (default
Ctrl-B D for tmux, or
Ctrl-A D for screen), and disconnect SSH while your process continues in tmux/screen.
Later when you connect with SSH again, you can then attach to your multiplexer (e.g.