To control how the window manager (compiz) controls resizing requires a bit of poking around in the various gsettings values.
In particular there is the resize compiz plugin with a mode parameter which you can fiddle with.
By default it is set to "0" which is "Normal" and equates to whole window resizing
gsettings set org.compiz.resize:/org/compiz/profiles/unity/plugins/resize/ mode 0
A value of "1" is enough to stop whole window resizing and switch to displaying a frame
gsettings set org.compiz.resize:/org/compiz/profiles/unity/plugins/resize/ mode 1
A value of "2" displays a frame with a blur of the window border
gsettings set org.compiz.resize:/org/compiz/profiles/unity/plugins/resize/ mode 2
A value of "3" shrinks the window during resizing:
gsettings set org.compiz.resize:/org/compiz/profiles/unity/plugins/resize/ mode 3
wmctrl
maybe)? Slow and ugly and error-trial like, but it would work until another solution is found.