Comment 4 for bug 1197754

stgraber@dakara:~/data/code/lxc/lxc$ lxc-start-ephemeral -o blah -d | grep "lxc-console" | awk '{print $NF}'
blah-psrfp_3s

Not the prettiest thing ever, but definitively doable with current lxc-start-ephemeral.
I won't be spending more time on lxc-start-ephemeral though as we'll have the new lxc-copy there soon that will take-over most if not all of it (lxc-start-ephemeral will likely be gone in 2.0).

So marking this fix-released as the above does work.